Amount Of Substance 1 Flashcards
Which number on the periodic table is always used to calculate Ar/Mr
The top number on the periodic table is always used for Ar/Mr
Why do scientists now use carbon-12 as the scale for Ar instead of hydrogen
Because the mass spectrometer has allowed us to measure the masses of individual isotopes extremely accurately. One twelfth of the relatives atomic mass of carbon-12 is given a value of exactly one.
Define relative isotopic mass
The mass of an atom of an isotope of an element on a scale where an atom of carbon-12 is exactly 12
Define relative atomic mass
The average mass of an atom of an element on a scale where an atom of carbon-12 is exactly 12
Define relative molecular mass
The average mass of a molecule on a scale where an atom of carbon-12 is exactly 12.
What is the equation for calculating relative atomic mass
Ar= sum of (isotope mass x isotope abundances) / total abundance
How do you calculate relative molecular mass (Mr)
Add up the relative atomic masses (Ar) of each of the elements present in the molecules.
How do you calculate relative formula mass (Mr)
Same as relative molecular mass (just says formula as ionic compounds don’t have molecules). You add the relative atomic masses of all of the atoms present in the compound.
What is avogadros constant
The number of atoms in 12g of carbon-12.
It is 6.022 x 10^23
Define mole
The amount of a substance that contains 6.022 x 10^23 particles/atoms.
What is the link between the Ar or Mr of a compound and moles
The Mr or Ar of a substance in grams contains exactly one mole of particles of that substance.
What is the equation linking molar mass, Mass and moles
Moles= mass (g)/ molar mass (gmol ^-1) Or moles= mass (g)/ Mr
What is molar mass (simply)
The Mr in gramsmol^-1
What are the units for molar mass
gmol^-1
What symbol is used to represent amount of substance
n
What equation links molecules, moles and avogadros constant
Number of molecules= moles x avogadros constant
What equation links moles, concentration and volume
Moles= concentration ( moldm^-3) x volume (dm^3)
What is a solution
A solution is a compound consisting of a solvent with a solute dissolved in it.
What does the concentration of a solution tell us
How much solute is present in a known volume of solution.
What are concentrations of solutions measured in
Mol dm^-3
What does a concentration of one mol dm^-3 mean
That there is one mole of solute per cubic decimetre of solution.
What is the volume of one mole of any gas at room temperature and pressure
24 dm^3
What is Boyles law
The product of pressure and volume of a gas is constant as long as temperature remains constant.
Pressure (P) x Volume (V) = constant
What is Charles’ law
The volume of a gas is proportional to its temperature as long as the pressure remains constant.
Volume (V)/ temperature (T)= constant
What is Gay-lussac’s law (also called the constant volume law)
The pressure of a gas is proportional to its temperature as long as its volume remains constant.
Pressure (P)/temperature (T)= constant.
What equation does combining the relationships between Charles’ law, Gay-Lussac’s law and Boyles law give us
(Pressure (P) x Volume (V))/Temperature (T)= constant for a fixed mass of gas.
What is the ideal gas equation in words
Pressure x volume = number of moles x gas constant R x temperature
What is the simple letter version of the ideal gas equation
PV=nRT
What does the letter P represent in the ideal gas equation PV=nRT
Pressure
What does the letter v represent in the ideal gas equation PV=nRT
Volume
What does the letter n represent in the ideal gas equation PV=nRT
Number of moles n
What does the letter R represent in the ideal gas equation PV=nRT
Gas constant R which is 8.31 JK^-11mol^-1
What does the letter T represent in the ideal gas equation PV=nRT
Temperature
What units must be used for pressure P when using the ideal gas equation PV=nRT
Pascals
What units must be used for temperature T when using the ideal gas equation PV=nRT
Kelvins
What units must be used for volume V when using the ideal gas equation PV=nRT
M^3
What is the gas constant R in the ideal gas equation PV=nRT
8.31 JK^-1mol^-1
How do you convert a temperature in degrees Celsius into kelvins
Add 273
How do you find the Mr of a compound if you know the number of moles in a given mass
Divide the number of moles by the mass to get the value for the mass of one mole which is the same as Mr.
What is empirical formula
The empirical formula is the formula that represents the simplest whole number ratio of the atoms of each element present in a compound.
Describe how to find the empirical formula of a compound
1) Find the masses of each of the elements present in a compound (by experiment)
2) Work out the number of moles of atoms of each element.
3) Convert the number of moles of each element into a whole number ratio.
What should you do if you have a difficult ratio of moles of elements that are not easy to convert when calculating empirical formula
Divide each number by the smallest number
How do you find the molecular formula of a compound from its empirical formula
To find the number of units of the empirical formula in the molecular formula,divide the relative molecular mass by the relative mass of the empirical formula. The multiply the empirical formula by this number.
What is the stoichiometry of a reaction
The ratio in which the reactants react to form products in simple whole numbers. (The number in front of the molecules in a balanced chemical equation)
What does the state symbol (aq) mean
Aqueous- the compound is dissolved in water
What is the ionic equation whenever an acid reacts with an alkali
H+ (aq) + OH- (aq) —> H20 (l)
What is the equation for atom economy
Atom economy= mass of desired products/ total mass of reactants x 100
Describe the difference between percentage yield and atom economy
- The atom economy gives us a theoretical value for the amount of reactants wasted in forming the desired product
- Percentage yield tells us about the practical efficiency of the process- how much product is lost in relation to the total theoretic product that could be made (this could be from the practical process of obtaining a product or as a result of reactants that do not go to completion)
What is the equation for percentage yield
Percentage yield= mass/moles of product formed/ total theoretical mass/moles x 100
What charge does a hydrogen ion have
H+
What charge do group one metal ions have
M+
What charge do group two metal ions have
M(2+)
What charge do group three metal ions have
M (3+)
What charge does an Iron (II) ion have
Fe2+
What charge does an iron (III) ion have
Fe(3+)
What charge does a Copper (I) ion have
Cu1+
What charge does a copper (II) ion have
Cu2+
What charge does a silver (I) ion have
Ag+
What charge does an ammonium ion have
(NH4) + (+1 charge)
What charge does a halogen ion have
X-
What charge does a sulphide ion have
S 2-
What charge does an oxygen ion have
O 2-
What is the formula and charge of a sulphate ion
(SO4) 2- (2- charge)
What is the formula and charge of a nitrate ion
(NO3)-
What is the formula and charge of a hydroxide ion
OH-
What is the formula and charge of a phosphate ion
(PO4) 3- (3- charge)
What is the formula and charge of a sulphite ion
(SO3) 2- (2- charge)
What is the formula and charge of a nitrite ion
(NO2) -
What is the formula and charge of a carbonate ion
(CO3) 2- (2- charge)
What are the products of a reaction between a metal and an acid
Metal + Acid —> Salt + Hydrogen
What are the products of a reaction between a metal hydroxide and an acid
Metal hydroxide + Acid —> Salt + Water
What are the products of a reaction between a Metal Oxide and an acid
Metal Oxide + Acid —> Salt + Water
What are the products of a reaction between a metal carbonate and an acid
Metal Carbonate + Acid —> Salt + Water + Carbon dioxide
What is the charge of an aluminium ion
Al 3+
What is the charge of a zinc ion
Zn 2+
What are polyatomic ions
Ions that consist of two or more atoms
Why is using the molecular formula not practical when looking at large molecules such as giant ionic lattices
In large ionic compounds, crystals are formed consisting of giant ionic lattices. We cannot use molecular formula to represent this because
1) the number of atoms would be too large
2) bigger crystals would have more atoms than smaller ones despite being the same compound.
What is the equation used to calculate concentration (include units)
Concentration (mol/dm^3) = Amount of substance (mol) / volume (dm^3)
How do you convert a value from cm^3 to m^3
Divide by one million
How do you convert a value from dm^3 to m^3
Divide by one thousand
What do we assume when we describe an ideal gas
- that the gas molecules are tiny compared to the spaces between them
- there are no forces acting between the gas molecules
- the gas molecules move randomly
- when the gas molecules collide, the collisions are elastic
What is atmospheric pressure
101,000 Pa or 101kPa
How do you work out the amount of substance in moles of a compound in a given mass
Divide the mass in grams by the compounds molar mass (Mr is gmol^-1)
How do you work out the number of atoms in a given mass of an element
Use moles=mass/Mr to find the number of moles of the compound and multiply this by avogadros constant (6.022 x 10^23)
How do you work out the number of atoms in a given mass of a compound
- Use moles=mass/Mr to find the number of moles of the compound.
- Multiply this by avogadros constant (6.022 x 10^23) to find the number of molecules of the compound present.
- Then multiply this by the number of atoms present in each molecule which can be worked out from the molecular formula.
How do you work out the number of molecules of a compound present in a given mass of the compound
- Use moles=mass/Mr to find the number of moles
- Multiply this by avogadros constant (6.022 x 10^23) to find the number of molecules present.
How do you convert a volume from dm^3 to cm^3
Multiply by 1000
How do you convert a volume from cm^3 to dm^3
Divide by 1000
How do you convert a value from m^3 to cm^3
Multiply by one million
How do you convert a value from m^3 to dm^3
Multiply by 1000
How do you work out the concentration when given the number of moles and volume of the solution
- Make sure that the units for volume is dm^3
- divide the number of moles by the volume using concentration=moles/volume
How do you work out the number of moles in a solution when given concentration and volume
- make sure that the concentration is in (moldm^-3) and the volume is in (dm^3)
- Calculate the number of moles using moles= concentration x volume
How do you calculate the concentration of a solution when given the number of moles and volume
- make sure the volume is in (dm^3)
- Calculate the concentration using concentration= moles/volume
How do you calculate the concentration of a solution when given the volume of the solution and the mass of solute dissolved in it
- Calculate the Mr of the solute using the periodic table and molecular formula
- Use the mass and Mr to calculate the number of moles of the solute present using moles=mass/Mr
- Make sure that the volume is in (dm^3)
- Use concentration=moles/volume to calculate the concentration.
What do we consider room temperature
20 degrees Celsius
When given the mass of a named metal that reacts with a named base at room temp and pressure, how do you work out the volume of gas produced
- write out the balanced chemical equation (knowing the reactions that take place between metals and different bases)
- Use moles=mass/Mr to calculate the number of moles of the metal that reacts
- Use this and the balanced chemical equation to calculate the number of moles of the gas produced.
- Multiply the number of moles of gas produced by 24 as a mole of any gas at room temperature occupies 24dm^3
How do you calculate the volume of a gas when given the number of moles, the temperature and the pressure
- Use the ideal gas equation and arrange it to V=nRT/P
- convert the pressure into pascals
- convert the temperature into Kelvins
- Substitute these into the equation to calculate the volume in m^3
How do you calculate the pressure of a gas when given the number of moles, volume and temperature of the gas.
- Use the ideal gas equation and rearrange to get P=nRT/V
- convert the volume into m^3
- Convert the temperature into kelvins
- Substitute into the ideal gas equation to calculate the pressure in Pascals
How do you calculate the volume of gas produced when a mass of a named metal reacts with a named base. You are given the temperature and pressure (not room temp)
- Write out the balanced chemical equation
- use moles=mass/Mr to calculate the number of moles of the metal that react.
- Use the balanced chemical equation to find the number of moles of the gas produced.
- Convert the temperature into kelvins
- convert the pressure into pascals
- Rearrange the ideal gas equation for volume to get V=nRT/P
- Substitute moles, temp and pressure into this to get the volume in m^3
How do you calculate the number of moles of a gas when given the temperature, pressure and volume of the gas.
- Use the ideal gas equation and rearrange it to get n=PV/RT
- Convert the temperature into Kelvins
- Convert the pressure into Pascals
- Convert the volume into m^3
- Substitute these values into the ideal gas equation to calculate the number of moles.
How do you calculate the mass of a named compound that has reacted with a named gas when given the chemical equation, volume of the gas, temperature and pressure of the reaction
- rearrange the ideal gas equation to get n=PV/RT
- Convert the pressure into pascals
- Convert the temperature into Kelvins
- Convert the volume into m^3
- Substitute these values into the ideal gas equation to calculate the number of moles of gas that reacted.
- Use the balanced equation to work out how many moles of the compound reacted.
- Use the molecular formula and periodic table to calculate the Mr of the compound.
- Use mass=moles x Mr to calculate the mass of the named compound.
Describe the 8-step method of the experiment that allows us to use the ideal gas equation to determine the molar mass/relative molecular mass of a chemical
1) Take a gas syringe with a small cap on the end and use a mass balance to find the mass of the empty syringe and cap.
2) remove the cap and draw a small volume of the chemical into the syringe.
3) Replace the cap to seal the chemical in the syringe
4) Reweigh the gas syringe containing the chemical plus the cap.
5) Calculate the mass of the chemical in the syringe by subtracting the initial mass of the empty syringe plus the cap from the mass of the syringe containing the chemical plus the cap.
6) Boil the chemical by placing the syringe into a beaker of boiling water.
7) Once the chemical has boiled, read the volume of the gas from the scale on the gas syringe
8) Use the mass and volume of the chemical to work out the relative molecular mass.
What is the problem with the method for the experiment that allows us to use the ideal gas equation to determine the molar mass of a chemical. How do we fix this.
- Placing the syringe containing the chemical in a beaker of boiling water only works for chemicals with a lower boiling than 100 degrees Celsius as that is the boiling point of water
- If the chemical has a boiling point greater than 100 degrees Celsius, an oil bath would have to be used.
How do you calculate the molar mass/relative molecular mass of a chemical when given the mass of it that evaporated, the volume produced, the temperature and the pressure of the reaction.
- rearrange the ideal gas equation for moles to get n=PV/RT
- convert the volume of the gas into m^3
- convert the temperature into kelvins
- Convert the pressure into Pascals
- Substitute these values into the ideal gas equation to get the number of moles of the chemical.
- then use moles=mass/Mr to get the Mr/molar mass of the chemical.
How do you work out the empirical formula of a compound when given the masses or percentages of each element present in the compound
- divide the mass/percentage of each element by the elements Mr to get the number of moles of each element.
- write the number of moles as a ratio and divide by the smallest one to get an easy ratio.
- ensure that the final ratio is in whole integers by multiplying if needed.
- write as a formula.
How do you work out the molecular formula of a compound when you have its empirical formula and its relative molecular mass (Mr)
- Calculate the Mr of the empirical formula
- Divide the Mr of the compound by the Mr of the empirical formula (scale factor between the two)
- multiply the number of atoms of each element in the empirical formula by this number to get the number in the molecular formula.
What is water of crystallisation
When water molecules form an essential part of the crystal structure of some ionic compounds.
What is a hydrated compound
A compound that contains water of crystallisation
What is an anhydrous compound
A compound that does not contain water of crystallisation.
What happens when a hydrated compound is heated
The water is removed to leave the anhydrous compound.
How do you work out the value of x in front of Y.xH20 in a named hydrated ionic compound Y when you have the relative formula mass of the hydrated compound.
- Work out the Mr of just the compound Y without the water
- subtract this from the relative formula mass of the whole hydrated compound to get the relative mass of the water present.
- Use moles=mass/Mr to calculate the number of moles of water (Mr of water is 18)
- the number of moles is the value of x in these compounds.
How do you work out the value of water of crystallisation x when you have the starting mass of a hydrated compound that was heated until the mass stopped decreasing to give a value for the final mass.
- Subtract the final mass from the starting mass to get the mass of water present in the hydrated compound
- Divide this by the Mr of water (18) to calculate the moles of water present.
- The final mass is the mass of the anhydrous compound.
- Divide this by the Mr of the compound to calculate the moles of ionic compound present.
- Divide the moles of water by the moles of the ionic compound to get the value for water of crystallisation x
Why is the compound heated to a constant mass when calculating water of crystallisation
- to ensure that all of the water is removed From the compound
Describe method of the experiment that allows us to calculate the value x for water of crystallisation in a hydrated compound
1) Weight the empty boiling tube and record it’s mass
2) Place around 2cm depth of the hydrated compound into the boiling tube and reweigh.
3) Record the mass of the compound and boiling tube.
4) Heat the boiling tube and contents using a Bunsen burner
5) Reweigh at regular intervals until a constant mass is reached
6) record the mass of the test tube and contents once a constant mass is reached.
7) Use this value to calculate the value for water of crystallisation.
Why would the value of water of crystallisation be lower than expected
Not all of the water molecules were driven off during heating- the tube wasn’t heated to a constant mass.
Why would the value for water of crystallisation be greater than expected
This suggests that the compound has undergone further decomposition once the water was driven off- the anhydrous compound may have decomposed to a different compound.
What is the equation for calculating atom economy
Atom economy= Mr or mass of desired product/total Mr or mass of all reactants X100
For what type of reaction is the atom economy always 100%
A reaction with one product
What is different about the chemical equation for atom economy
The big numbers in the chemical equation count when calculating atom economy
What is the equation for calculating percentage yield
Yeild/maximum theoretical yeild x100
How do you work out percentage yield of a product when given the mass of a reactant and the mass of product produced
- write out the balanced chemical equation for the reaction
- Calculate the number of moles of the reactant using moles=mass/Mr
- use this to find the number of moles of the product
- Multiply this by the Mr of the product to calculate the maximum theoretical mass
- Substitute the actual mass of the product produced and theoretical mass into the equation for percentage yield.
