# Safety in the Lab is ALWAYS important.. In the following situation, which course of action is best: A student is heating water in a beaker on a hotplate.

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Safety in the Lab is ALWAYS important.

In the following situation, which course of action is best: A student is heating water in a beaker on a hotplate. She notices that the beaker appears to be developing a crack. She decides to… 1.Ignore it because the water is nearly boiling anyway. 2.Tell her partner to be careful, because she is afraid it may break. 3.Turn off the heat and inform the teacher immediately. 4.Turn off the heater, get a new beaker, and try it all over again.

Observation or Inference? Observations are descriptions or measurements using senses and instruments. Inferences are best guesses based upon observation. Inference is also known as: hypothesis, educated guess, prognostication…

The temperature now is 27 o C. It will rain today. Mr. Pearl has grey hair. He is an old man. Earth’s Outer Core is 6000 o C. White Plains has a lot of metamorphic rock.

Measurements Measurements allow us to quantify…add value to observations. Measurements have a quality…a unit. Measurements require instruments. The standard of the instrument is its scale.

The collapse of the I-35 bridge in Minneapolis in 2007 killed 13 people. The bridge collapsed because of poor maintenance and measurement! This is an extreme example of poor measurement. Let’s see how to avoid simple mistakes to simple questions.

SCALES

Remember…… A measurement includes a value “each interval equals 0.2” A scale includes a unit “3 means 3 what?” …3 boogers?

Based on these readings, the temperatures are (1)Wet bulb = 16 o C, Dry Bulb = 16 o C (2) Wet bulb = 15 o C, Dry Bulb = 25 o C (3) Wet bulb = 19 o C, Dry Bulb = 24 o C (4) Wet bulb = 17 o C, Dry Bulb = 24 o C

What is the scale of this graduated cylinder? 5 mL 50 mL / 10 =

What is the scale of this graduated cylinder? 0.1 mL 1mL / 10 = What is the volume of liquid? 6.3 mL

In each case determine: a) the scale 0.1 mL 0.5 mL 0.2 mL

In each case determine: b) the volume 52.5 mL 11.5 mL 6.6 mL

What is the scale for the Y-axis (Total column water vapor)? 0.25 cm

Powers of Ten x 10 x 10 x 10 x 10 ……

3.0 x 10 1 3.0 x 10 2 4.0 x 10 3 2.7 x 10 5 Rounded off!

3.0 x 10 -1 3.0 x 10 -2 5.7 x 10 -9 Rounded off!

456.4 37.99 464 299,000,000 or 2.99 x 10 8

HOW MUCH?

DENSITY is the amount of mass (matter or STUFF) in a certain volume (space).

Leaves float on water But so does the whole tree!

Density values can be calculated by the formula: Density = mass / volume -- Or -- D= m / v

Compared to Earth’s continental crust, Earth’s mantle is (1) thinner and more dense (2) thinner and less dense (3) thicker and more dense (4) thicker and less dense

If an object is “regular” (like the classroom), then volume can be calculated… V = L x W x H V = cm x cm x cm = cm 3

If an object is liquid (like water), then volume can be measured… V = mL

If an object is “irregular” (like a rock), then volume can be measured by water displacement…

According to an electronic balance, this rock has a mass of 13.7 g. What is the rock’s density? mL

What is the density of mineral sample A? (1) 12.0 g / cm 3 (3) 4.0 g / cm 3 (2) 3.0 g / cm 3 (4) 0.33 g / cm 3

What is the density of mineral sample B? (1)12.0 g / cm 3 (3) 4.0 g / cm 3 (2) 3.0 g / cm 3 (4) 0.33 g / cm 3

13.5 g / mL Three materials are dropped into a container of mercury (13.5 g / mL ). The first material is water (1 g / mL ). The other two are shown below the picture. m = 15 g V = 18 mL m = 78 g V = 5 mL What order will they take? water

The graph here shows the relationship between mass and volume for three samples, A, B, and C, of a given material. What is the density of this material? (1) 1.0 g/cm3 (3) 10.0 g/cm3 (2) 5.0 g/cm3 (4) 20.0 g/cm3

If density is a property of matter, can it change? YES!!! If the temperature changes

Same matter (mass) but increased volume!

BTW …… If matter is cooled, the reverse happens!

Mathematically… If a block has a volume of 10 cm 3 and a mass of 20 g… D = m / v = 20 g / 10 cm 3 = 2 g / cm 3 If heated, the block’s volume becomes 15 cm 3 but the mass remains at 20 g… D = m / v = 20 g / 15 cm 3 = 1.33 g / cm 3 When temperature, volume, density.

FIRST EFFECT HOT air expands, becomes less dense, and rises

HOT air balloon

Heat air Let air cool WHY?

SECOND EFFECT HOT magma expands, becomes less dense, and rises

THIRD EFFECT HOT substances expand, change phase, AND becomes less dense.

SOLID LIQUIDGAS Adding heat will make a solid change to a liquid and then change to a gas Removing heat (cooling) does the reverse MOST DENSE LESS DENSE LEAST DENSE

Which graph correctly demonstrates the relationship between heat and density?

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