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**SCIENTIFIC MEASUREMENT**

To calculate Density, you have to know how to measure volume and mass properly and accurately!

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**Reporting Measurements**

Using significant figures Report what is known with certainty Add ONE digit of uncertainty (estimation) By adding additional numbers to a measurement – you do not make it more precise. The instrument determines how precise it can make a measurement. Remember, you can only add ONE digit of uncertainty to a measurement. Davis, Metcalfe, Williams, Castka, Modern Chemistry, 1999, page 46

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**The instrument determines the amount of precision of the data.**

62.4 .00g What is the certain measurement here? What is the estimated measurement here?

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**Using Significant Figures reflects precision by estimating the last digit**

52 ml .8 ml What is the certain measurement? What is the estimated measurement?

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**Measurements in the Lab:**

Example B Example A 40 mL 30 mL 20 mL 20 mL 30 mL 10 mL Graduated Cylinder marked in 1.0 mL increments. you record volume as mL 1. If the glassware is marked every 10 mLs, as is this beaker, the volume you record should be in whole mLs. (Example A) 2. If the glassware is marked every 1 mL, as is this graduated cylinder, the volume you record should be in tenths of mLs. (Example B) 3. If the glassware is marked every 0.1 mL, as is this buret, the volume you record should be in hundredths of mLs. (Example C) Beaker marked in 10 mL increments. The volume you write in your lab report should be 13 mL 0 mL 1 mL 2 mL Example C Buret marked in 0.1 mL increments. You record volume as 0.67 mL

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**Practice Measuring cm 1 2 3 4 5 4.5 cm cm 1 2 3 4 5 4.54 cm cm 1 2 3 4**

1 2 3 4 5 4.5 cm cm 1 2 3 4 5 4.54 cm PRACTICE MEASURING Estimate one digit of uncertainty. a) 4.5 cm b) * 4.55 cm c) 3.0 cm *4.550 cm is INCORRECT while 4.52 cm or 4.58 cm are CORRECT (although the estimate is poor) The better marks the better we can estimate. Scientist always understand that the last number measured is actually an estimate cm 1 2 3 4 5 3.0 cm Timberlake, Chemistry 7th Edition, page 7

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Finding VOLUME

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Finding VOLUME What is VOLUME? The amount of space that a 3-dimensional object or substance takes up. Anything that exists is made of matter and therefore has volume…(takes up space)

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The OBJECTS

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The OBJECTS Let's try this one first!

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Formula/Equation? Volume = L xW x H Length = 6cm

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Finding Volume Volume = L x W x H Length = 6cm Height = 4cm

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**Volume = L x W x H Finding Volume Length = 6cm Width = 2cm**

Height = 4cm

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**Volume = L x W x H Finding Volume SO MULTIPLY 'EM! Length = 6cm**

Width = 2cm Height = 4cm SO MULTIPLY 'EM!

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Volume = L x W x H = 6 cm x 2 cm x 4 cm = 48 cm3

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**So, the VOLUME (the amount of space that this 3 dimensional object takes up) is 48 cm3**

Nice work.

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The OBJECTS Now, let's try this one

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**Find the VOLUME Can't do L x W x H… …it's an irregular shape.**

things that make you go hmmmm...

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**The METHOD – Finding Volume by Water Displacement**

-40mL -35mL -30mL -25mL -20mL -15mL -10mL -5mL

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**1. Note the water level 20 mL -40mL -35mL -30mL -25mL -20mL -15mL**

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**2. Place the object in liquid**

-40mL -35mL -30mL -25mL -20mL -15mL -10mL -5mL

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**3. Watch the object displace the water it is place into…**

-40mL -35mL -30mL -25mL -20mL -15mL -10mL -5mL

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**4. Note difference in water level**

35 mL -40mL -35mL -30mL -25mL -20mL -15mL -10mL -5mL 20 mL

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**The water level changed 15mL**

35 mL -20 mL 15 mL -40mL -35mL -30mL -25mL -20mL -15mL -10mL -5mL 20 mL We can say the rock displaced 15mL of water

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**But wait, it gets better! 3 1mL = 1cm so... 3 15mL = 15cm -40mL -35mL**

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Volume of our rock… 3 = 15cm Great work!

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DENSITY Density is defined as mass per unit volume. It is a measure of how tightly packed and how heavy the atoms are in an object. Density is the ratio of mass to volume You can think of Density as the amount of stuff per unit of space Density is the amount of matter within a certain volume.

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**Density is the measure of the “compactness” of a material**

How close the atoms or molecules are to each other. More than “heaviness” - density includes how much space an object takes up!! All substances have density including liquids, solids, and gases. We need to be able to think about density visually, logically and mathematically Bread slice and compacted bread in large flask of water

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**Visually - Which one is more dense?**

Demonstration: Atoms in a substance Which square is more dense? circle one Masses are / are not equal Volumes are / are not equal

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**Visually - Which one is more dense?**

Now… which one is more dense? Masses are / are not equal Volumes are / are not equal

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**Logically - What would take up more space. A kilogram of feathers…**

Logically - What would take up more space? A kilogram of feathers….. or a kilogram of steel? ROCKS - pass around OR

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**DENSITY Mathematically**

Even though it has a numeric value, Density is a considered a (qualitative) intensive property of matter. does NOT depend on the quantity of matter. this is similar to temperature Contrast with (quantitative) extensive property depends on quantity of matter. mass and volume are quantitative. Styrofoam Brick

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**Mathematically DETERMINING DENSITY**

Regular Shapes – mass, then determine the volume by formula/equation EX: cubes, rectangular prisms, cylinders, spheres, cones, etc. Irregular shapes – mass, then measure displacement of a liquid (usually water) by that irregularly shaped object Since we know that 1 mL has the same volume as 1 cm3, we can make an easy conversion! Density = mass (g) volume (cm3 or mL)

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**Equation to Calculate a Substance’s DENSITY**

For our terms and purposes: Mass is usually expressed in grams Volume usually expressed in cubic centimeters (cm3) or milliliters (mL) Density may be expressed in other units, but you will learn about them in Physics and Chem….

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**DENSITY - an important and useful (qualitative) intensive physical property**

Aluminum Platinum Mercury 13.6 g/cm3 21.5 g/cm3 2.7 g/cm3

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**Density Calculations of:**

Regularly Shaped Solids: mass = triple beam or electronic balance volume = measure (l x w x h) 2. Irregularly Shaped Solids: volume = water displacement

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**Density Calculations of:**

3. Liquids: mass = tare graduated cylinder, mass liquid volume = read graduated cylinder We will perform labs on all of these types of density calculations!

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**Learning Check – Mathematical Calculations of Density**

Osmium is a very dense metal. What is its density in g/cm3 if g of the metal occupies a volume of 2.22 cm3? 1) 2.25 g/cm3 2) 22.5 g/cm3 3) 111 g/cm3

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**Learning Check – Mathematical Calculations of Density**

Placing the mass and volume of the osmium metal into the density setup, we obtain D = mass = g = volume 2.22 cm3 = g/cm3 = 22.5 g/cm3

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**Learning Check – Mathematical Calculations of Density**

Which diagram represents the correct order of liquid layers in the cylinder? (K) Karo syrup (1.4 g/mL), (V) vegetable oil (0.91 g/mL,) (W) water (1.0 g/mL) 1) 2) 3) W K V V W K W V K

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**Learning Check – Mathematical Calculations of Density**

The density of octane, a component of gasoline, is g/mL. What is the mass, in kg, of 875 mL of octane? 1) kg 2) 614 kg 3) 1.25 kg

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**Learning Check – Mathematical Calculations of Density**

If blood has a density of 1.05 g/mL, how many liters of blood are donated if 575 g of blood are given? 1) L 2) 1.25 L 3) 1.83 L 4) 548 L

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**Learning Check – Logical Thinking about Density**

Fact: Water has a density of 1.0 g/ml and mercury (Hg) has a density of 13.6 g/ml. Which is heavier, a quart of water or a quart of mercury? If we have equal volumes of two different substances, then the one with the greater density will have the greater mass.

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**Which is heavier, a ton of feathers or a ton of bricks?**

Neither Feathers Which is larger? If two objects have the same mass, the one with the higher density will be smaller.

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**Factors Affecting Density Write the relationship statements.**

Temperature – What substance is the exception to this rule? Pressure – Add several drops of red food color to each of two 250-mL Erlenmeyer flasks; fill them with warm tap water. (If tap water is not warm, heat some tap water on a hot plate to °C.) Add several drops of blue food coloring to each of the other two 250-mL Erlenmeyer flasks; fill them with cool tap water. Predict the outcome when one flask is inverted over the other. Place a paper card on top of the vessel filled with warm water. Invert the flask making sure to hold the card in place. Stack it on top of one of the cool water flasks. Remove the card. Remain prepared to catch the flasks. ** Visual here. Place a paper card on top of the flask filled with cool water. Invert the flask making sure to hold the card in place. Stack it on top of the other warm water flask. Remove the card. Wide mouth containers may also be used.

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**Factors Affecting Density**

A solid solutes dissolved into liquid solutions – the density change depends on the concentration and kind of substances mixed together. Write the relationship statement:

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**Factors Affecting Density**

Atomic mass – Different atoms have different atomic masses. Write the relationship statement.

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**Applying What You’ve Learned – Let’s think about the Density of Water!**

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**Question #1: At what temperature is water most dense?**

Find this information on your ESRT’s! Hint: Look for a section about the Properties of Water… Question #2: Use this chart to explain why ice floats on water. Use data from the chart to support your answer!!!! Question #3: Use this chart to explain what happens to average sea level when the ocean’s average temperature increases.

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**Density Table SINK or FLOAT In Water? (D = 1.0 g/mL) Float Float Float**

(alcohol) Float (fuel)

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Specific Gravity The density of a material or substance, relative to another substance Expressed in a ratio: water = 1.0 g/cm3 Water is the substance to which we compare other substances Also known as SPECIFIC GRAVITY Since we dived the density of any substance by 1.0 g/cm3, the specific gravity value is equal to the density of the substance. What are the units for specific gravity? Relative Liquid densities: Oil, colored water, and corn syrup in a graduated cylinder. An H2O ice cube floats in liquid H2O but sinks in rubbing alcohol. A can of diet coke floats in water while a can of regular coke sinks (can determine density of sugar versus NutraSweet using balance).

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