KCSE 2026 CHEMISTRY PAPER 1 PREDICTIONS

Ajouté : 2026-05-05

[00:00:01]Your wrist flicks the air like [music] a sail catching wind.

[00:00:06]We step on hot coals where the ocean [music] ends.

[00:00:10]And palm fronds cut the light into moving lace. [music] I don't know your name, Mr. David here.

[00:00:20]Remote exam, chemistry paper one.

[00:00:23]Chemistry paper one.

[00:00:31]Complete the table by writing the observation made when aqueous ammonia and aqueous sodium sulfate is added to solutions containing calcium and aluminum ions as follows.

[00:00:45]So, calcium ion. If you add aqueous ammonia, what observation do you expect?

[00:00:53]For calcium, in ammonia, there will be no white precipitate.

[00:00:58]No No white precipitate.

[00:01:04]Because calcium forms a white precipitate with the sulfate to form calcium sulfate.

[00:01:09]To form calcium sulfate, so there will be a white a white precipitate.

[00:01:16]A white precipitate, but always write in full.

[00:01:19]I'm writing short, but always write white precipitate in full.

[00:01:23]So, for aluminum, for aluminum, there will be a white precipitate which is insoluble in excess.

[00:01:33]For uh sodium sulfate, we do not have a white precipitate in aluminum ion, so there's no white precipitate.

[00:01:41]For iron two, it will form a green precipitate with aqueous ammonia.

[00:01:46]A white A green precipitate insoluble in excess.

[00:01:50]But uh aqueous sodium sulfate will not form a green precipitate, so there will be no green precipitate with uh sulfate. But for iron two, we expect green. Iron three, we expect brown precipitate.

[00:02:12]Suppose we had a zinc here, zinc two ions here. It will form a white precipitate soluble in excess. White PPT soluble in excess. Here, there will be no white precipitate.

[00:02:29]A group of compounds called chlorofluorocarbons have a wide range of uses, but they do also have harmful effects to the environment.

[00:02:39]Give one use of chlorofluorocarbons.

[00:02:42]State one harmful effect and uh of chlorofluorocarbons on the environment.

[00:02:55]They are used uh refrigerants as as a refrigerant in fridges.

[00:03:03]Also, air conditioners conditioners conditioners.

[00:03:08]Also, they are used as propellants in aerosols. Aerosol cans.

[00:03:14]Then, one of the harmful effects of them is that they depression of ozone layer.

[00:03:31]Element U has atomic number 12, while element V has atomic number 16.

[00:03:37]How do they How do their melting point of their oxides compare? Explain the answer.

[00:03:46]Element U, atomic 12 and atomic 16.

[00:03:51]How do their oxides compare?

[00:03:55]Element two, that is magnesium, it will form magnesium oxide.

[00:03:59]Element 16 is sulfur, it will form sulfur.

[00:04:04]The oxide is sulfur four oxide. So, how do these uh compare? The melting point How do these Of course, this one will have higher melting point because it is a solid and this one is a gas, therefore it will have low melting point.

[00:04:21]The oxide of U has higher that is the oxide of magnesium has a higher melting point.

[00:04:27]The The oxide of U, which is the oxide of magnesium, has a higher melting point than that of the oxide of V, which is sulfur.

[00:04:39]Magnesium oxide has a higher has a giant ionic structure with strong ionic bond.

[00:04:49]While sulfur four oxide have simple molecular structure with weak van der Waals forces. That is the reason.

[00:05:05]Define the term solubility. Define the term solubility.

[00:05:12]This is the maximum mass of a solute that can dissolve in 100 g of water at a specific temperature or at a given temperature. That's what we call the solubility.

[00:05:33]40 g of a saturated solution yields 15 g of salt uh when evaporated to dryness. Calculate the solubility of the salt.

[00:05:47]So, 40 g of a saturated solution.

[00:05:49]Remember saturated solution is saturated solution contains What is a saturated These are the things you need to understand.

[00:06:02]A saturated solution contains a solute plus a solvent.

[00:06:08]You get that? Because a saturated solution is a solution which contains a solute which is dissolved until it will not dissolve anymore.

[00:06:16]So, if uh 40 g of a saturated solution If this solution is 40 g, which is saturated, is supposed to contain a solute and a solvent.

[00:06:26]Then now we can get if the solute yield 15 g of the salt, so 15 plus X, which is the solvent. X is mass of the solvent.

[00:06:36]Now, we can get the mass of the solvent, so that is 40 minus 15 will give us X.

[00:06:44]That one will be 25 g of the solvent.

[00:06:50]Now, when you are asked calculate solubility, solubility is in 100. So, we will say 25 g 25 g of the solvent was able to dissolve in 15 g of the solute.

[00:07:08]Now, what about 100 g of the solvent? Because 100 From the definition, you need to understand what is solubility.

[00:07:16]So, what about 100? So, the answer will be 100 times 15 you divide by 25 and this one here here four and that one will be 60 g.

[00:07:30]g per 100 L.

[00:07:32]Very correct. 60 g.

[00:07:35]g per 100 of water.

[00:07:38]>> [clears throat] >> Hydrogen gas can be prepared by passing steam over heated magnesium ribbon as shown.

[00:07:48]Yes, that is hydrogen. Explain why the delivery tube must be removed from beneath the water before heating is stopped. It is to avoid sucking back of water. So, if this water is is If the This one is removed carelessly, it will suck water into this hot apparatus and they are likely to break.

[00:08:22]Is to prevent suck suck back of water into the hot test tube which it would because it to break or to crack.

[00:08:34]Explain why sodium metal is not suitable in this experiment. Sodium reacts violently with the steam or the water, so we cannot use that one.

[00:08:48]Give two reasons why hydrogen is not commonly used as a fuel.

[00:08:52]Why is hydrogen not used as a fuel?

[00:08:55]It is because it is highly flammable and explosive as well as it is as well as it is expensive. It is expensive.

[00:09:05]State Graham's law of diffusion. State Graham's law of diffusion. You must have all the laws of gases. Law of gases should be That is the Boyle's law, the Charles' law, the Graham's law should be in your head always.

[00:09:22]The rate of diffusion of a gas is inversely proportional to the square root of its density at constant [snorts] temperature and pressure.

[00:09:37]Explain why a balloon filled with helium gas deflates faster than a balloon of the same size filled with argon gas.

[00:09:47]Deflates faster.

[00:09:51]Right?

[00:09:52]What is the reason behind that? Helium has a lower lower molecular mass compared to argon. It is It diffuses out through the balloon pores faster.

[00:10:10]Helium has a lower molar mass compared to argon.

[00:10:17]So, it diffuses out through the balloon pores faster. That is the reason.

[00:11:48]Iron filings Iron tube Iron Iron filing Using iron filings, describe the experiment that can be conducted to show that oxygen is present in air.

[00:12:12]Place moist iron filings in a graduated beaker.

[00:12:16]Invert the beaker over a trough of water as length with air and iron filings between the between them. Leave the setup for store for several of days. Leave the setup for several days until the iron rusts completely and the water level stops rising.

[00:12:49]The water rises to occupy the space of the oxygen used during rusting.

[00:13:00]Using iron filings, describe the experiment that could be conducted to show that oxygen is present in the air.

[00:13:04]That is it.

[00:13:15]Hydrogen chloride gas can be prepared by reacting sodium chloride with an acid.

[00:13:22]Write the equation for the reaction between sodium chloride and the acid.

[00:13:32]Sodium chloride, that is the solid.

[00:13:35]Sodium chloride plus uh sodium sulfuric acid con give you sodium hydrogen sulfate plus HCl.

[00:13:48]Give two chemical properties of hydrogen chloride gas.

[00:13:56]It reacts with ammonia gas to form dense more dense white fumes, ammonium chloride.

[00:14:04]It dissolves in water to form a strong acidic solution, HCl, that turns blue litmus paper to red.

[00:14:28]Calcium oxide can be used to dry ammonia gas.

[00:14:33]Explain why calcium oxide is not used to dry hydrogen chloride gas. Hydrogen chloride Hydrogen chloride gas is acidic. So, it will react with calcium oxide, which is a base.

[00:14:48]Calcium oxide is basic. It reacts with HCl, so that which is acidic to form calcium chloride and water. So, you cannot do that.

[00:15:06]The figure below shows a chart.

[00:15:09]We have crude oil, process A, naphtha, process B, ethene, ethene oxidation compound E, from ethene reaction C, ethanol, then from ethene process D, polyethene.

[00:15:27]Name process A B. Name process A.

[00:15:31]Uh B Where is B? B is here.

[00:15:37]And Okay, those are the names. Those are the processes we have to name.

[00:15:47]Process A is fractional distillation and B is cracking, thermal cracking.

[00:15:57]Long carbon chains, so this is crude oil to naphtha, we have fractional distillation.

[00:16:04]From naphtha, long carbon chain to small carbon chain, we do uh cracking. Which type you can use? Even thermal cracking or catalytic cracking.

[00:16:13]Then we have ethene. Ethene will undergo process E reaction D to form this E.

[00:16:18]That is polymerization.

[00:16:20]Then ethene to ethanol.

[00:16:25]State one condition necessary for the reaction C to occur.

[00:16:33]Condition C.

[00:16:38]That is phosphoric acid, high temperature of 300, high pressure.

[00:17:00]Compound C has the following percentage composition by mass, 39, 38.7, 7.5 hydrogen and this.

[00:17:09]Given that the 0.05 moles of compound E has a mass of this, calculate the molecular formula of E.

[00:17:31]So, you draw that table, carbon, hydrogen because it is a Now, and 7.10 the remaining you subtract 100 and you get that.

[00:17:43]From there you get the number of moles, the mole ratio, which is 1 to 3, and that is the empirical formula.

[00:17:49]Then we have been given that the compound E has a mass of this.

[00:17:56]So, if that is the mass, we can get the molecular mass. Molecular mass is equal to moles uh mass over moles. That's how you get the molar mass. The molar mass is 62.

[00:18:09]Therefore, you get 31 and you get the empirical the molecular formula now.

[00:18:29]The table below shows some property of three substances.

[00:18:34]Complete table by filling in the types of forces and structure in each.

[00:18:47]Melting point, boiling point, electrical conductivity in molten and solid, types of force structure.

[00:18:55]So, X poor poor, Y good good, Z poor in solid, good in in molten.

[00:19:15]So, if it is poor poor, then it is a molecular It is a molecular a simple molecular structure.

[00:19:21]Simple molecular structure, then the type of forces van der Waals forces.

[00:19:27]Uh Y is good good. So, if it is good good, it must be uh a metallic a metal.

[00:19:35]Therefore, it is a metallic bond and it could be that the giant uh metallic It is giant ionic or giant metallic the structure.

[00:19:46]Poor in solid state, good in molten.

[00:19:50]That one is ionic bond, giant ionic structure.

[00:20:00]The elements sulfur, phosphorus, and chlorine are regarded as having simple molecular structures.

[00:20:07]Write the molecular formula of sulfur.

[00:20:11]Write the molecular formula of sulfur, phosphorus.

[00:20:30]Sulfur and phosphorus.

[00:20:38]Arrange these three elements in order of their increasing melting point. Explain the trend.

[00:20:47]Sulfur, phosphorus, and then chlorine.

[00:20:50]Melting point is uh increases as the molecular size increases. As the molecular mass As the molecular size or as the mass increases because van der Waals forces become stronger as the molecular mass increase.

[00:21:18]Use the energy bond below and I bond energies below to calculate the energy the heat of reaction of burning methane of burning methane.

[00:21:31]So, the equation has been given for you here.

[00:21:35]This is the burning of methane.

[00:21:37]So, you need to do write it here and open the structure in open structure.

[00:21:52]Use the bond energies below to calculate the heat of reaction for burning methane. And now the equation for methane has been provided here.

[00:22:02]Methane plus oxygen, two moles of oxygen forms. Now, you need to open to write the open structure of methane, then oxygen there are two moles, so two moles of that. Then carbon, we should know that is how it carbon dioxide this how it is. It has a double bond here.

[00:22:22]Then oxygen is uh water is is written like this. Now, from there you need to know the bond energy the four bond of formation energy uh bond breaking and the bond formation energies. You should know which one is exothermic and which one is endothermic.

[00:22:48]So, heat change is this one and you find your answers that.

[00:23:02]When excess lead to nitrate solution was added to solution containing sodium chloride, the precipitate formed was found to weigh 5.5. Determine the amount of sodium chloride in the solution.

[00:23:25]So, you write the equation, balance the equation.

[00:23:29]Then get the molar mass of lead chloride by adding the sodium lead you lead you have been given 207. All of that you get that is 278. Number of moles of lead chloride you get it as this. Then you use the mole ratio and you get the number of moles of sodium chloride. The number of moles of sodium chloride will be twice that of the lead chloride because of the ratio 2 to 1. So, this is the number of moles of of lead chloride. Then now you use uh the formula um mass is equal to moles over FM and then you use the formula the triangle.

[00:24:08]Because we are looking for mass of determine the uh determine the amount determine the amount of sodium chloride that is the mass.

[00:24:20]We know this is moles mass moles RFM. So, to get mass it is moles times RFM of sodium chloride.

[00:24:31]And that is you give you 2.31.

[00:24:45]Starting with copper copper metal describe how solid sample of copper two carbonate can be prepared. Copper two carbonate is is an insoluble salt. So, you need to remember that.

[00:25:01]React copper metal with concentrated nitric acid with nitric acid to form copper two nitrate solution. Add sodium carbonate solution to to copper two nitrate solution to precipitate out copper two carbonate copper carbonate.

[00:25:22]Filter the mixture to obtain the copper two carbonate.

[00:25:28]Yes, wash the residue as a residue. Wash the residue with distilled water and dry it between two filter papers.

[00:25:43]A sample of water in a beaker was found to boil at this at atmospheric. Assuming that the thermometer was not fault, explain the why this happened. So, water should be people is should boil at 100 degrees.

[00:25:58]So, what happened? So, we are assuming that the thermometer was not fault. What must have happened?

[00:26:09]The water is impure. The presence the presence of impurities raises the boiling point of water above 100. That is very correct.

[00:26:26]Describe the experimental procedure that can be used to extract oil from nut seeds.

[00:26:33]Nut seeds.

[00:26:38]Crush or grind the nut seeds using a mortar and a bell pestle to increase the service area. Add suitable solvent which could be propanol or ethanol and stir to dissolve and stir to dissolve the oil stir to dissolve the oil. Filter the mixture to remove solid remains.

[00:27:05]Leave the filtrate in the sun in the sun uh to evaporate the solvent leaving to to evaporate the solvent leaving the oil behind.

[00:27:27]State again Charles's law.

[00:27:33]When gases react they do so in volumes which bear a simple ratio to one another and the to the for to the volume of the product the volumes of the product provided that the temperature and the pressure remains constant.

[00:28:10]180 of nitrogen dioxide was reacted with 40 oxygen. Calculate the total volume of gas at the end of the reaction.

[00:28:20]First, we need to write the reaction a balanced equation.

[00:28:25]Balanced equation, then use the volume ratio that is Gay-Lussac's law for you to get that.

[00:28:35]This is the application of Gay-Lussac's law.

[00:28:59]>> [snorts] >> Calcium oxide dilute colorless solution heat to dryness step two solid F.

[00:29:18]Colorless solution excess carbon dioxide substance C. Give the name of the process that took place in step one.

[00:29:25]Calcium oxide plus HCl colorless solution that is neutralization reaction.

[00:29:32]Neutralization reaction.

[00:29:36]Uh give the name of substance C substance C.

[00:29:41]So, this one will form a colorless that is calcium chloride calcium chloride with the with carbon dioxide to form substance which is calcium carbonate.

[00:29:54]That is this calcium carbonate.

[00:29:57]Calcium hydrogen carbonate. Yes, calcium hydrogen carbonate.

[00:30:05]Give one use of substance F.

[00:30:08]Substance F.

[00:30:12]So, this is when you dry So, calcium chloride you will have dry it to dryness, you will form solid calcium chloride which is used as >> [clears throat] >> a drying agent.

[00:30:29]Use it as a drying agent.

[00:30:33]Yes, drying agent.

[00:30:47]When a sample of concentrated sulfuric acid was left in an open beaker in a room temperature for 2 days, the volume was found to have increased slightly.

[00:31:00]What property of concentrated sulfuric acid is shown by the above reaction?

[00:31:08]So, it absorbs water from the atmosphere. That's why it is increasing.

[00:31:12]So, it is showing a property that we call hygroscopic.

[00:31:18]>> [clears throat] >> Acid absorbs water vapor from the atmosphere which increases [clears throat] the volume.

[00:31:29]State one use of concentrated sulfuric acid that depends on the property above.

[00:31:37]Used as a drying agent. That's correct.

[00:31:45]Name the apparatus that can be used to measure fixed volume of a solution.

[00:31:50]Fixed volume of a solution you can use the pipette. Pipette measures only 25. You can use that. Measure fixed amount of You can use a pipette as range. Even a burette if it measures only 50.

[00:32:07]Volumetric flask. Yes.

[00:32:13]Lower a burning piece of magnesium ribbon into a gas jar. A deflagrating spoon. A deflagrating spoon.

[00:32:26]Store and keep substances free from moisture. A desiccator. That is correct.

[00:32:35]Explain why high temperatures is required for nitrogen to react with oxygen.

[00:32:42]The triple bond of the nitrogen need to be broken.

[00:32:47]This the triple bond which are very strong has to be broken. For that, nitrogen molecules have very strong triple covalent bond.

[00:32:57]A high amount of energy is required to break them before the atom reacts with oxygen.

[00:33:07]Dry ammonia and dry oxygen were reacted as shown.

[00:33:12]What purpose of the glass What's the purpose of the glass wool?

[00:33:18]Glass wool.

[00:33:27]To provide a large surface area for the reaction.

[00:33:32]To cover to hold the catalyst in place.

[00:33:38]What products would be formed if red hot platinum was introduced into a mixture of ammonia and oxygen?

[00:33:48]Nitrogen two oxide.

[00:33:50]Water will be formed.

[00:34:01]The diagram below shows an incomplete setup to prepare sulfur four oxide in the lab. Remember sulfur four oxide is collected by downward delivery. That is what we are testing.

[00:34:16]You need to dry the gas using concentrated sulfuric acid and then collect it by downward delivery. Sulfur four oxide being denser than air.

[00:34:36]Identify solid H.

[00:34:40]Identify solid H. Solid H is sodium sulfite.

[00:34:44]Calcium sulfite.

[00:34:46]I or calcium sulfite. Any of them.

[00:34:54]Temporary water hardness can be removed by boiling. What is hard water?

[00:35:02]This is the water that contains dissolved salts of calcium or magnesium and it does not lather easily with soap.

[00:35:14]Write the chemical equation to show how temporary hardness water hardness is removed by boiling.

[00:35:23]Calcium hydrogen carbonate heat calcium carbonate water and that or magnesium hydrogen carbonate when heated decomposes to form magnesium carbonate carbon four oxide and water and that's how it is removed. State one advantage of hard water. Provides calcium ions which are essential for the strengthening to strengthen the bones and the teeth in humans.

[00:35:53]What is a fuel?

[00:35:57]A fuel is a substance that produces useful energy when it undergoes a chemical or a nuclear reaction.

[00:36:09]Calculate the heating value of ethanol if its molar enthalpy of combustion is 13 this one.

[00:36:18]So, first get the RFM of ethanol. You need to get the RFM of ethanol. Then you divide by this by the RFM and you are done.

[00:36:29]So, the RFM or RMM of ethanol is this one. So, heating value is equal molar enthalpy divided by the molar mass and that is it.

[00:36:43]Use the chemical equation below to answer the question. This ammonia reacting with water to form ammonium ion. That is a ammonium ion and hydroxide hydroxide ions. The acid Identify the acid in the forward reaction. Explain. The acid in the forward reaction.

[00:37:04]Water donates It is water which donates a proton, hydrogen ions, to a to form ammonium ion.

[00:37:20]In the forward reaction, water behaves as an acid.

[00:37:24]Because if it donates an ion.

[00:37:28]A base in the forward reaction.

[00:37:34]Ammonia.

[00:37:36]It accepts a proton to form ammonium ion.

[00:37:49]What is the relationship between the volume and the pressure of a gas?

[00:37:59]The volume of a fixed mass of a gas is inversely proportional to its pressure at constant temperature.

[00:38:08]Whose law is that?

[00:38:17]Your guess is as good as mine.

[00:38:22]3 L of oxygen gas at one atmosphere pressure were compressed to two atmospheres at a constant temperature. Calculate the new volume occupied.

[00:38:35]Volume occupied by the oxygen gas.