Somerset Academy - Central Miramar Campus



Density Calculations with Significant DigitsIntroductionDensity is a measurement of how compact a substance is. The unit of density we will use most often in chemistry is grams/milliliter, or g/mL.Significant Figures in Addition and SubtractionWhen adding or subtracting two or more numbers, the answer should be rounded to the least number of decimal places in your data. Example: Add the following masses: 42.56 g + 39.460 g + 4.1 gSolution: 42.56 g 39.460 g + 4.1 g 86.120 g Rounded answer = 86.1gComplete the following problems, rounding the answer to the correct number of decimal places. Calculator AnswerRounded Answer14.1g + 0.54g_______________ _______________1.001mL + 5.1mL + 10.55mL_______________ _______________20lb - 0.5lb - 1.4lb = _______________ _______________Significant Figures in Multiplication and DivisionWhen multiplying or dividing two or more numbers, the answer should be rounded to the least number of significant figures in your data. Example: Calculate the area of a 5.2cm x 9.80cm rectangleSolution: 5.1cm (2 significant figures) x 9.80cm (3 significant figures) 50.96cm2 Rounded answer = 51cm2 (2 significant figures)Complete the following problems, rounding the answer to the correct number of significant figures. Calculator AnswerRounded Answer10.0m/s * 5.9s _______________ _______________25cm * 25cm_______________ _______________125m2 / 25m _______________ _______________Calculating DensityDensity cannot be easily measured directly. However, it can be calculated by measuring the volume and mass of the substance, then using the following formula: right635000To find the volume of a solid object, it is placed (carefully) into a graduated cylinder containing a pre-measured amount of liquid. What is the volume of the rock shown to the right? Show all calculations, and follow the rules of measuring with significant figures.The same rock is placed on a triple-beam balance, with the following result. Record the mass using the correct number of significant digits.Calculate the density of the rock using the formula at the beginning of this section. Follow the rules for division with significant figures.Practice ProblemsSolve each of the problems below using the density equation. Show work, and follow rules for significant figures.A 5.00 cm3 sample of gold has a mass of 96.5 g. Calculate the density of gold.You measure the mass of a large piece of wood to be 75.1g. The wood has a volume of 78.5cm3. Calculate the density of the wood.The density of table sugar is 1.59 g/cm3. What is the volume of 7.85 g of sugar?Aluminum has a density of 2.70 g/cm3. Calculate the mass of a solid piece of aluminum whose volume is 1.50 cm3.Silver has a density of 10.5g/cm3. Aluminum has a density of 2.7g/cm3. If you have a 2cm x 2cm x 2cm cube of a silver metal that has a mass of 21.6g, is it aluminum or silver? ................
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