Change sign key

Enter the exponent of 10 through the keyboard If the exponent is negative, also press the "change sign key (common symbols are CHS and +/-) It is important that you don t press the - key (i e, the subtract key)... 

If you simplify this with a hand calculator, enter -4.3 through the keyboard (enter 4.3 followed by tl j change-sign key), then proceed as on p 16. This gives [H+l = 5 01 X 10- ... 

If we want to enter a negative number, the number is entered first, and then its sign is changed with the change sign key, not the subtraction key. 

To enter a number in exponential form, use the special key, EE or EXP, meaning X 10 to the power, not the multiplication key. To enter a negative number, press the change sign key before EE or EXP to enter a negative exponent, press the change sign key after EE or EXP. 

Special note for electronic calculator users To determine the negative of the logarithm of a quantity, on some calculators, enter the quantity, press the LOG key, then press the change-sign key, -f/—. On other calculators. 

The change-sign key converts 3 to —3 before the two numbers are multiplied. 

A.23. What value will be obtained if 4 is entered on a calculator and then the change-sign +/— key is pressed twice ... 

Ans. In order to solve this problem one must use either log tables or a hand calculator which has a logarithm function key. With a calculator, enter the value of 0.00263, and press the log key. The result will read —2.58. Now press the change sign key, +/—, and the answer will read 2.58, which is the pH. 

The problem resolves itself into the question What is the antilog of -2.7, or what is the numerical value of 10 raised to the power of -2.7 Your calculator should have a 10, or antilog key. It is used as follows first enter 2.7, then press the change sign key +/-. Next press the 10 key and read the answer, 0.002 M. If your calculator does not have an antilog function, do the calculation as described in Chap. 1 on the use of a logarithm table. 

On your calculator, there are four keys that are used for basic mathematical operations. The change sign key is used to change the sign of a number. 

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