Classify each substance as a pure substance or a mixture. If it is a pure substance, classify it as an element or a compound. If it is a mixture, classify it as homogeneous or heterogeneous.

a. sweat b. carbon dioxide

c. aluminum d. vegetable soup

Solution 37E: 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 (a) 601 kg, There are three significant figures. This is because , zero is between the non zero digits. So zero is also a significant figures along with non zero digits. (b) 0.054 s Here significant figures are two. This is because, zero in the beginning is not significant. So it is counted only two non zero digits as the significant figures. (c) 6.3050 cm Here significant figures are five. Zeros between nonzero digit are significant whereas the zero at the end of a number is also significant. (d) 0.0105 L Here significant figures are three. Zeros in the beginning of a number is non significant before and after the decimal point. But Zeros between nonzero digit are significant. (e) 7.0500 * 10-3 m3 Here significant figures are five. The exponential value is not significant. Zeros between nonzero digit are significant whereas the zero at the end of a number as well as right of the decimal point is also significant. (f) 400 g. Here significant figures is one. This is because it has no decimal point But if we need more significant figures. Then the number should be converted into exponential notation. 400 = 4.0 x 10 , it has two significant figures.