Problem 41E

Determine whether each molecular diagram represents a pure substance or a mixture. If it represents a pure substance, classify the substance as an element or a compound. If it represents a mixture, classify the mixture as homogeneous or heterogeneous.

Solution 41E All digits of a measurement including uncertain number are called significant figures. Significant figures = all certain digits + one uncertain digit The rules for determining the significant figures are (i) Zeros between nonzero digits are always significant (ii) Zeros at the beginning of a number are never significant. (iiI) Zeros at the end of a number are significant if the number has a decimal point only. Rules for find out the significant figures for multiplication and division When multiplication and division is carried out, the results must contain the same significant figures with the measured one which has the fewest significant figures. That is way the result should be rounded off when it contains more correct significant figures. Rules for find out the significant figures for Subtraction and addition The decimal places will be same for the result as the the measurement with the fewest decimal places.That is way the result should be rounded off when it contains more correct significant figures. Rules for rounding off the significant figures If the result contains more number of correct significant figures, then the result should be rounded off. (i) To round off the number, we have to look carefully the leftmost digit which one, we are going to be removed. (ii) If the removing leftmost digit is less than 5, then the number should be keep unchanged (iii) if the removing leftmost digit is 5 or more than 5, then the preceding number is increased by one. (a) 14.3505 + 2.65 = 17.0005 The round off number is 17.00 ( round off to two significant figures) Thus the result has two decimal places which is due to the lowest decimal place of measurement 2.65 (b) Here we have to calculate the final value by using the following operation 952.7 - 140.7389 =811.9611 = 812.0 (round off to three significant figures) The round off number is 812.0, This is because the leftmost digit 9 is more than 5, so the the preceding number is increased by one. Thus the final result has one decimal places which is due to the lowest decimal place of one of the measurement value 9 52.7 (c) Here we have to calculate the final value by using the following operation (3.29 x 10 )(0.2501) 4 = 0.822829 x 10 = 0.823 x 10 ( round off to three significant figures) The round off the number is 0.823 x 10 , This is because the leftmost digit 8 is more than 5, so the the preceding number is increased by one. Thus the final result is three significant figures which is due to the lowest significant figures of 4 one of the measurement value (3.29 x 10 ) (d)0.0588/0.677 Here we have to calculate the final value by using the following operation 0.0588/0.677 = 0.0868537 = 0.0869 (( round off to three significant figures) -2 = 8.69 x 10 The round off the number is 8.69 x 10 , This is because the leftmost digit 5, so the the preceding number is increased by one. Thus the final result is three significant figures which is due to the lowest significant figures of one of the measurement value (0.677)