Log & Antilog Tricks in Chemistry | No Calculator, No Log Table

[00:00:00]Log and antilog for chemistry. I will teach you my personal trick to solve any question of log and antilog in chemistry without using log table and calculator.

[00:00:11]Even if you don't know anything about log, still you will be able to solve any question. You don't need to memorize any formula. Using my personal trick, it is very easy and fun to calculate log and antilog question. First of all, I will teach you super easy trick to learn log table from 1 to 10. We know that log 1 is equal to 0 and log 10 is equal to 1.

[00:00:36]Just remember that log 9 is equal to 0.95.

[00:00:41]Now listen carefully. Below log 9, I write 5, then 6, 7, 8, 9, 13, and 17.

[00:00:50]Here, 0.95 - 0.5 = 0.90. 0.90 - 0.6 is equal to 0.

[00:01:00]84. 0.84 - 0.7 is equal to 0.77.

[00:01:05]0.77 - 0.8 is equal to 0.69. 0.69 - 0.9 is equal to 0.60.

[00:01:14]0.60 - 0.13 = 0.47 and 0.47 - 0.17 = 0.30.

[00:01:24]Thus, using this super easy trick, we can easily learn log table from 1 to 10.

[00:01:30]Now I will teach you type 1 question.

[00:01:33]For example, consider these question. In case of first question, we can see that this 3 is the power. I take the power and I write it here. I put plus sign.

[00:01:45]The remaining part is log 5. I write it here as log 5. According to the log table, log 5 is equal to 0.69.

[00:01:55]So I write 3 + log 5 is equal to 0.69.

[00:02:00]After addition, I get 3.69.

[00:02:04]This log 5 into 10 raised to the power 3 is equal to 3.69.

[00:02:11]In case of log 3 into 10 raised to the power -4, I take this power -4 and I write it here. Plus, the remaining part is log 3. I write log 3. According to the log table, log 3 is equal to 0.47.

[00:02:28]I write -4 + 0.47.

[00:02:32]After calculation, I get -3.53.

[00:02:36]This log 3 into 10 raised to the power -4 is equal to -3.53.

[00:02:43]In case of log 10 raised to the power 8, we can also write this as log 1 into 10 raised to the power 8. As usual, I take the power 8 and I write it here. Plus, the remaining part is log 1. According to the log table, log 1 is equal to 0. I get 8. This log 10 raised to the power 8 is equal to 8. Finally, I take this power 2 and I write it here. Plus, the remaining part is log 9. I write it here. We know that log 9 is equal to 0.95.

[00:03:19]I write 2 + 0.95.

[00:03:22]After calculation, I get 2.95.

[00:03:26]This log 9 into 10 raised to the power 2 is equal to 2.95.

[00:03:32]Hence, note it down this important question. Now, we will learn type 2 question. For example, consider this question. In case of first question, I take this -5 and I write it here. Plus, the remaining part is log 3.8. I write it here. Now, listen carefully. Log 3.8 lies between log 3 and log 4. The value of log 3 is 0.47 and that of log 4 is 0.60.

[00:04:03]So, the value of log 3.8 is between 0.47 and 0.60.

[00:04:10]We know that log 3.8 is also nearer to log 4. It means that its value is also nearer to 0.6 0. So, I guess that log 3.8 is approximately equal to 0.57 or 0.56.

[00:04:30]Remember that we only guess the value.

[00:04:32]It totally depends on you whether you write 0.56 or 0.57.

[00:04:39]After calculation, I get -4.43.

[00:04:43]Thus, log 3.8 into 10 raised to the power -5 is approximately equal to -4.43.

[00:04:53]In the second question, I take this three and I write it here. Plus, the remaining part is log 5.4. Log 5.4 is between log 5 and log 6. Secondly, it is nearer to log 5. Its value is between 0.60 and 0.69.

[00:05:13]Let I guess that its value is 0.72 or 0.73.

[00:05:19]I write 3 + 0.72.

[00:05:22]After calculation, I get 3.72.

[00:05:25]Thus, log 5.4 into 10 raised to the power 3 is approximately equal to 3.72.

[00:05:33]In the third question, this is a four-digits number. In such types of questions, we convert it to scientific notation. I write log 7.834 into 10 raised to the power 3. As usual, I take this three and I write it here.

[00:05:51]The remaining part is log 7.834.

[00:05:55]Here, I select only 7.8.

[00:05:59]We can see that log 7.8 lies between log 7 and log 8. Secondly, log 7.8 is nearer to log 8. It means that the value of log 7.8 lies between 0.84 and 0.90.

[00:06:16]Let I guess the value of log 7.8 as 0.88.

[00:06:23]I write 3 + 0.88.

[00:06:26]After calculation, I get 3.88.

[00:06:30]Thus, log 7834 is approximately equal to 3.88.

[00:06:37]In the last question, this is a decimal number. I will convert it to scientific notation. I write log 4.52 into 10 raised to the power -2. As usual, I write -2 here. The remaining part is log 4.52.

[00:06:54]I select only 4.5.

[00:06:57]Log 4.5 is the midpoint of log 4 and log 5. Let I guess its value as 0.65.

[00:07:06]I write -2 + 0.65.

[00:07:09]After calculation, I get -1.35.

[00:07:14]Thus, log 0.0452 is equal to -1.35.

[00:07:20]Now, I will show you the power of this trick by solving real chemistry question.

[00:07:26]Find the pH of soft drink if concentration of hydrogen ions is 3.8 into 10 raised to the power -3 M. Well, we know that pH is equal to negative log of hydrogen concentration. The concentration of hydrogen ion is already given. I write pH is equal to negative log the concentration of hydrogen ions is 3.8 into 10 raised to the power -3.

[00:07:52]As usual, I write negative into I take this -3 and I write it here. The remaining part is log 3.8.

[00:08:01]We know that log 3.8 lies between log 3 and log 4. Secondly, it is nearer to log 4. Let I guess its value as 0.56.

[00:08:12]I write negative into -3 + 0.56.

[00:08:17]Here, -3 + 0.56 equals to -2.44.

[00:08:23]I write negative into -2.44.

[00:08:27]After calculation, I get 2.44.

[00:08:31]Thus, the pH of this soft drink is 2.44, which is acidic. Therefore, using my personal trick, we can easily crack any log question in chemistry without log table and without calculator.

[00:08:47]Finally, we will learn all about antilog. We know that antilog is a reverse process of a log. For example, log 2 is equal to 0.3 and log 5 is equal to 0.67.

[00:09:01]Then, if I ask you to find antilog of 0.30 and antilog of 0.67, can you guess the answer? Well, the reverse of 0.30 is 2. The reverse of 0.69 is 5. Let me solve some questions, which will clear your all confusion. For example, consider this question. In case of the first question, I write it as antilog 4 + 0.69.

[00:09:31]Now, listen carefully. I take this 4 and I write it 10 raised to the power 4.

[00:09:37]Secondly, we know that log 5 is equal to 0.69.

[00:09:42]Then antilog of 0.69 equals 5. I write 5 into 10 raised to the power 4. Thus, antilog of 4.69 is equal to 5 into 10 raised to the power 4. In case of second question, I write it as antilog 8 + 0.90.

[00:10:02]As usual, I write this 8 as 10 raised to the power 8. We know that log 8 is equal to 0.90.

[00:10:10]Then antilog of 0.90 is equal to 8. I write 8 into 10 raised to the power 8.

[00:10:17]Thus, antilog of 8.90 is equal to 8 into 10 raised to the power 8.

[00:10:25]In case of third question, I write antilog -6 + 0.70.

[00:10:32]I mean -6 + 0.70 is equal to -5.30.

[00:10:39]Now, I write this -6 as 10 raised to the power -6. We know that log 5 is equal to 0.69.

[00:10:48]Then antilog of 0.70 is approximately equal to 5. I write 5 into 10 raised to the power -6.

[00:10:57]Thus, antilog -5.30 is approximately equal to 5 into 10 raised to the power -6.

[00:11:06]In the last question, I write antilog 3 + 0.74.

[00:11:11]I write this 3 as 10 raised to the power 3. Secondly, 0.74 lies between log 5 and log 6. Let I guess that 0.74 is approximately equal to log 5.6.

[00:11:27]Hence, antilog of 0.74 is approximately equal to 5.6.

[00:11:34]I write 5.6 into 10 raised to the power 3. Thus, antilog of 3.74 is approximately equal to 5.6 to 10 raised to the power 3.

[00:11:46]Finally, let me teach you an advanced concept of logarithm, which will help you a lot. Find value of X in the following question. Well, in case of first question, log X is equal to 3.30.

[00:12:00]We will transfer log from left-hand side to the right-hand side. Remember this very, very important point. When we transfer log from one side to another side, it becomes antilog and vice versa.

[00:12:15]Let me repeat it. When we transfer log from one side to another side, it becomes antilog and vice versa. So, I write X is equal to antilog 3.30.

[00:12:27]I write X is equal to antilog 3 + 0.30.

[00:12:32]Or, I get X is equal to 2 into 10 raised to the power 3. In the second question, I transfer antilog from the left-hand side to the right-hand side. I get X is equal to log 6.95.

[00:12:47]We know that log 6.95 is approximately equal to 0.83.

[00:12:54]I get X is equal to 0.83.

[00:12:58]Therefore, using my personal tray, you can crack any question in chemistry without calculator and without log table.