DENSITY KHS 2014 Q) Which weighs more:- A kilogram of feathers or a kilogram of iron?

What is Density? Density is the Mass per unit Volume WoodWaterIron 1 cm 3 1 cm 3 1 cm 3 If you take the same volume of different substances, then they will weigh different amounts g1.00 g8.00 g Q) Which has the greatest mass and therefore the most dense? IRON

Density = Mass Volume g or kg cm 3 or kg 3 g/cm 3 or kg/m 3  = m V Example: Q) Liquid water has a density of 1000kgm -3, while ice has density of 920kgm -3. Calculate the volume occupied by 0.25kg of each. Density Equation: m V  V = m = 0.25 = m 3  1000 V = m = 0.25 = m 3  920

DENSITY OF A REGULAR SOLID Find the Mass of the solid on a balance. Find the Mass of the solid on a balance. Measure the three lengths and calculate the Volume. Measure the three lengths and calculate the Volume. (ie V = l x w x h ) Calculate the Density. Calculate the Density. 4.0 cm 2.0 cm 3.0 cm  = m = 240 =10.0 g/cm 3 V 24 m = 240 g

DENSITY g/cm 3 Aluminium2.70 Brass8.50 Iron7.86 Wood0.50 Slate2.80 Glass2.50 Lead11.3 Marble2.70 Wax0.89

DENSITY OF AN IRREGULAR SOLID Find the Mass of the solid on a balance. Find the Mass of the solid on a balance. Fill the Measuring Cylinder with Water to a known Volume. Fill the Measuring Cylinder with Water to a known Volume. Add the Object. Add the Object. Work out the Volume of Water that is displaced. Work out the Volume of Water that is displaced. Calculate the Density. Calculate the Density. 50 cm 3 80 cm 3 m = 360 g  = m = 360 =12.0 g/cm 3 V 30

DENSITY OF AN IRREGULAR SOLID OR use a Eureka Can to find the Volume. OR use a Eureka Can to find the Volume. Find the mass of the solid on a balance. Find the mass of the solid on a balance. Add water until just overflowing. Add water until just overflowing. Place a Measuring Cylinder under the spout. Place a Measuring Cylinder under the spout. Add the Object. Add the Object. Collect the Water and read off the Volume. Collect the Water and read off the Volume. Calculate Density Calculate Density m = 440 g 40.0 cm 3  = m = 440 =11.0 g/cm3 V 40

DENSITY g/cm 3 Aluminium2.70 Iron7.86 Brass8.50 Wood0.50 Slate2.90 Glass2.50

DENSITY OF A LIQUID Find the Mass of an empty Measuring Cylinder. Find the Mass of an empty Measuring Cylinder. Add a certain Volume of Liquid. Add a certain Volume of Liquid. Find the Mass of the Measuring Cylinder and Liquid Find the Mass of the Measuring Cylinder and Liquid Calculate the Mass of Liquid. Calculate the Mass of Liquid. How? How? Calculate Density of Liquid. Calculate Density of Liquid. Mass of Liquid = Mass of Measuring Cylinder and Liquid – Mass of empty Measuring Cylinder 25.0 g 20.0 cm g 45 – 25 = 20 g  = m = 20 =1.00 g/cm3 V 20

DENSITY OF A GAS Remove the air from a flask of a known Volume, using a vacuum pump. Remove the air from a flask of a known Volume, using a vacuum pump. Find its Mass. Find its Mass. Add the gas to be tested. Add the gas to be tested. Reweigh. Reweigh. The difference is the Mass of gas. The difference is the Mass of gas. Calculate Density. Calculate Density. To vacuum flask 1000 cm g170.0 g  = m = 20 = g/cm3 V = 20.0g

Warm-Up Estimate how long it would take for the entire world’s population to count up to one mole. Estimate how long it would take for the entire world’s population to count up to one mole. If you stacked a mole of marshmallows on top of each other and covered the United States how deep would the marshmallows be? If you stacked a mole of marshmallows on top of each other and covered the United States how deep would the marshmallows be? Working 48 hours a week it would take approximately 8 million years 600 miles

The Mole

What is the mole? The Mole: The amount of a substance that contains 6.02 x representative particles of that substance. The Mole: The amount of a substance that contains 6.02 x representative particles of that substance. The value of 6.02 x is known as Avagadro’s number The value of 6.02 x is known as Avagadro’s number In other words, the mole is a HUGE number! In other words, the mole is a HUGE number!

Question? If you had a mole of dollars and spent 1 billion dollars a second how long would it take for you to spend all of your money? If you had a mole of dollars and spent 1 billion dollars a second how long would it take for you to spend all of your money? $6.02 x 10^23 / $1,000,000,000 = 6.02 x 10 ^14 seconds $6.02 x 10^23 / $1,000,000,000 = 6.02 x 10 ^14 seconds 6.02 x 10 ^14 seconds / 60 seconds = x 10^13 minutes 6.02 x 10 ^14 seconds / 60 seconds = x 10^13 minutes x 10^13 minutes / 60 minutes = x 10^11 hours x 10^13 minutes / 60 minutes = x 10^11 hours x 10^11 hours / 24 hours = x 10^9 days x 10^11 hours / 24 hours = x 10^9 days x 10^9 days / 365 days = x 10^7 years x 10^9 days / 365 days = x 10^7 years It would take over 19 million years!! It would take over 19 million years!!

Why is a mole so big? Mass of atoms is so small you need many of them to have mass significant enough for people to weigh. Mass of atoms is so small you need many of them to have mass significant enough for people to weigh. The mass of an atom is measured in atomic mass units (AMUs) The mass of an atom is measured in atomic mass units (AMUs) Chemists picked a number equal to a certain mass of a certain element. Chemists picked a number equal to a certain mass of a certain element. The mass is grams and the element is carbon-12. The mass is grams and the element is carbon-12. Carbon-12 has 6 protons and 6 neutrons. Carbon-12 has 6 protons and 6 neutrons. The masses of all other elements are standardized against the carbon-12 atom. The masses of all other elements are standardized against the carbon-12 atom.

How is the mole useful? One atom of an element in AMUs = the mass of one mole of that element in grams One atom of an element in AMUs = the mass of one mole of that element in grams For example look at helium: For example look at helium: Number below helium is Number below helium is This indicates that the mass of one helium atom is AMU This indicates that the mass of one helium atom is AMU In addition, this indicates that if you have one mole of helium atoms those helium atoms would weigh grams In addition, this indicates that if you have one mole of helium atoms those helium atoms would weigh grams

Practice 1 mole = g Fe 1 mole = g Fe 1 mole = g H mole = g H x 10^23 atoms of Carbon = mol C x 10^23 atoms of Carbon = mol C x 10^23 atoms of Neon = mol Ne x 10^23 atoms of Neon = mol Ne /2 1/6