Chemistry · Some Basic Concepts Of Chemistry · NEET
No. Adding the exponents is only for MULTIPLICATION. For addition and subtraction you do NOT touch the exponent that way. First make both exponents equal, then add just the coefficients (the front numbers) and keep the same power of 10. Example: 5 x 10^3 + 2 x 10^3 = 7 x 10^3, not 10 x 10^6.
Not directly, because the powers (10^4 and 10^3) are different. Convert one so the powers match. Change 8.95 x 10^3 into 0.895 x 10^4. Now both are x 10^4, so add the fronts: 6.65 + 0.895 = 7.545. Answer = 7.545 x 10^4. Rule: move the smaller power UP to match the bigger power (or bring both to the same power).
Because the exponent tells you the place value. 10^4 means ten-thousands and 10^3 means thousands. Adding ten-thousands to thousands directly would be like adding rupees to paise without converting. Making the power equal puts both numbers on the same scale, so the front numbers can be safely added.
When you make the power BIGGER (3 to 4, that is +1), you must make the front number SMALLER by moving the decimal one place left. So 8.95 becomes 0.895. The number's true value stays the same: 0.895 x 10^4 = 8950 = 8.95 x 10^3. Rule of thumb: power goes up, coefficient goes down; power goes down, coefficient goes up.
Not in proper scientific notation. The front number must be between 1 and 10. Since 12.4 is more than 10, shift the decimal one place left and add 1 to the power: 12.4 x 10^5 = 1.24 x 10^6. Always fix the front number to be 1 to 9.99 at the end.
Same idea. Make powers equal. Bring 4.0 x 10^-32 to power -31: it becomes 0.40 x 10^-31 (power went up by 1, front moved left). Now subtract the fronts: 9.10 - 0.40 = 8.70. Answer = 8.70 x 10^-31. Negative exponents follow the exact same rule.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Make the powers of 10 equal. Convert the number with the smaller power so its exponent matches the larger one, then add the front numbers.
No. Adding exponents is only for multiplication. In addition and subtraction you keep one common exponent and only add or subtract the coefficients.
The coefficient must be between 1 and 10. If your result is like 12.4 x 10^5, shift the decimal left and raise the power by 1 to get 1.24 x 10^6.
Physical Chemistry problems (moles, Avogadro number 6.022 x 10^23, electron mass, wavelengths) often need you to add or subtract tiny or huge numbers. Getting the power-matching step wrong gives a completely wrong final answer.
No. The rule is identical for negative powers like 10^-31. You still match the exponents first, then add or subtract the coefficients.
