What are mass, volume, and density? Mass - Measurement of the amount of matter (or stuff) in an object. • Base unit is the gram There are 3 states of matter: Solid Liquid Gas Measuring Mass • Triple beam balance Digital top-loading scale Reading Sliders To maximize the number of digits in the measurement we estimate the last number. Since the slider is actually about halfway between 3.3 and 3.4, we record 3.35 300 g 70 g 3.35 g Weight and Mass Earth 1 gravity Nick’s mass Nick’s weight Jupiter 2.5 gravities 30kg On orbit 0 gravity 30kg Moon 1/6th gravity 30kg 300N 50N 750N 0 newtons 30kg Notice that Nick’s mass never changes. Nick is 30kg no matter where he goes! Volume The base unit for volume is the liter. 1) Volume of Regular Objects 5 cm • We can find the volume of regular shapes with the formula: Volume = length x width x height. 3 cm So a box 2 cm x 3 cm x 5cm would have a volume of: 30 cm3 2) Volume of Irregular Objects • Water displacement method. • Use a graduated cylinder to measure the volume of irregular objects. • Liquids form a curved surface in graduated cylinders called Meniscus. • Take your reading at the low point of the meniscus. 43.0 ml Water Displacement • Pour 7 ml of water in a graduated cylinder. If a rock causes the level to rise to 9 ml, the rock must have a volume of 2 ml. Volume units 1 cm3 = 1 ml 1 cm3 of water = 1 ml of water = 1 gram of water Which do you think would have the greater volume? The greater mass? Why? 1 kg of feathers 1 kg of rocks Water: Mass and Volume 1ml or 1cm3 of water = 1 g of water 50 ml or 50 cm3 of water has a mass of 50 grams 1000 g 1000 ml of water would have a mass of ________? Density 1. Density is defined as mass per unit volume. 2. It is a measure of how tightly packed the molecules are in an object. 3. Density is the amount of matter within a certain volume. Density A substance’s density DOES NOT CHANGE when the size of the sample increases or decreases. Al = 2.70 g/ml A solid substance has a measured volume of 75.0 ml. At STP it has a mass of 130.5 g. 1.74 g/mL Mg How do I Calculate Density? Density and specific gravity • Density often has units of grams per cubic centimeter (g/cm3). • Gram is the unit for mass. • Cm3 is the unit for volume. ***** 1ml = 1cm3 To find the density 1- Find the mass of the object 2- Find the volume of the object 3- Divide Density = Mass g Volume cm³ ALWAYS REMEMBER UNITS! Ways to Affect Density Change Mass AND Keep Volume Same Increase the mass increase density Decrease the mass decrease in density Which container has more density? A B Ways to Affect Density Change Volume AND Keep Mass Same Increase the volume decrease density Decrease the volume increase density Which container has more density? A B What 2 ways will INCREASE density? Keep the same mass AND decrease the volume Keep the same volume AND increase the mass Liquid Layers 1. If you pour together liquids that don’t mix and have different densities, they will form liquid layers. 2. The liquid with the highest density will be on the bottom. 3. The liquid with the lowest density will be on the top. 4. Objects or substances with MORE density will sink below objects or substances with LESS density. If you have 2 or more substances, the MORE dense substance will be on bottom The LESS dense substance will be on top The density of five liquids are measured as follows: – – – – – Liquid 1: 1.0 g/mL Liquid 2: 1.38 g/mL Liquid 3: 0.77 g/mL Liquid 4: 2.95 g/mL Liquid 5: 0.056 g/mL Liquid 5 Liquid 3 Liquid 1 Liquid 2 Liquid 4 Liquid Layers Check out this picture. Which layer has the highest density? Which layer has the lowest density? Imagine that the liquids have the following densities: – 10g/cm3. – 6g/cm3. 3g/cm3. 5g/cm3. 3 g/cm3 5 g/cm3 Which number would go with which layer? 6 g/cm3 10 g/cm3 Accuracy • How close a measured value is to an accepted value -Accuracy can be determined by just one measurement -Depends on the quality of the measuring device The density of water is 1.00 g/mL and a student calculated the density of water to be 0.99 g/mL. Precision •How close a series of measurements are to one another. -Precision is determined by more than one measurement -Depends on the skill of the person measuring The density of water is 1.00 g/mL .89 .87 .89 .88 .88 Examples of Precision and Accuracy: Low Accuracy High Precision High Accuracy Low Precision High Accuracy High Precision Percent Error • Accepted Value (also known as theoretical or true value) - a quantity used by general agreement of the scientific community - “what you are supposed to get” • Experimental Value (also known as the measured value) - a quantitative value measured during an experiment - “what you got” Percent Error Error = the difference between the accepted value and the experimental value Percent Error = the percent that a measured value differs from an accepted value % Error = (What you got) – (What you were supposed to get) x 100 (What you were supposed to get) Reference Table T Percent Error Practice 1. The boiling point of water is 100°C. During an experiment, water came to a boil at 97°C according to the thermometer that was being used. What is the percent error of the thermometer? 2. An experiment was performed to determine the density of water. The results of the experiment showed that water had a density of 1.15 g/mL. What was the percent error in this experiment? Percent Error Practice 3. An experiment was conducted to find the mass of one mole of carbon atoms. The results of the experiment showed that a mole of carbon atoms had a mass of 15.78 g. The accepted value of a mole of carbon atoms is 16.00 grams. What is the percent error in this experiment? 4. An experiment performed to determine the density of lead yields a value of 10.95 g/cm3. The accepted value for the density of lead is 11.342 g/cm3. Find the percent error.

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