Moles

What is the Empirical and molecular formula of a substance with the following %Compositiona. 92.3%C and 6.7%H (RMM = 52)b. 85.1% Br, 12.8% C and 2.1% H (RMM = 188 )

Calculations • A student took some 2M HCl and added 0.1

g of Mg to it.

a. Write an equation for the reaction taking place.

b. What is the minimum volume of HCl that was needed to react with all of the Mg

c. What volume of H2 was given off

d. What concentration of MgCl2 was formed?

Calculations • A student took 1cm3 of conc HNO3 and diluted it to

1dm3

• Exactly 25cm3 of 0.1M NaOH was required to neutralise 10cm3 of the diluted acid

a. Write an equation for the reaction taking place.b. What is the concentration of the diluted acidc. What is the concentration of the undiluted acid

Calculations • A student took 50cm3 of 2M HCl and added 1 g of

Limestone (impure CaCO3) to it. He collected 0.9dm3 of CO2

a. Write an equation for the reaction taking place.b. Show that the HCl was in excess (ie more moles than is needed)

c. What volume of CO2 should have been given off if the limestone was pure CaCO3

d. What is the % composition of CaCO3 in limestone

CalculationsA student took 1g of Citric acid C6H8O7.xH2O and dissolved it in 100cm3 of water. 10cm3 of this solution neutralised 14.3cm3 of 0.1M NaOHCitric acid is a tribasic acid and can be written as H3Y a.Write a balanced equation between citric acid and NaOHb.Show that the number of moles of citric acid that was neutralised was 4.77x10-4 c.Hence calculate the anhydrous mass of citric acid present in the 1g of hydrated citric acidd.Hence work out the value of x in C6H8O7.xH2O

Trends

• Explain whya. K has a lower Boiling Point than Cab. Si has a higher Boiling Point than Pc. Mg is a worse conductor than Ald. F atoms are smaller than N atomse. F atoms have a lower first IE than Ne atoms but a

higher first IE than Na atomsf. H2O has a lower melting point than Na2O but a

higher melting point than CO2

Shapes

• Draw dot ‘n’ cross diagrams ofSO3, Cl2S, PF3, SiCl4

Predict the shape of these 4 molecules

• Draw dot ‘n’ cross diagram of NaCl, MgCl2

Explain why MgCl2 has the higher Melting Point

Explain why neither conduct electricity when solid but both do when molten.

Reactivity

• Why is Mg less reactive than Ca?• How could you show this?• Why is I2 less reactive than Cl2 • How could you show this• Which decomposes at a lower temp CaCO3 or

MgCO3?

Observations

What do you see when you (write a balanced equation to show obs)a. Add CaCO3 to HCl

b. Add CaO to HClc. Add Mg to HCld. Heat CaCO3

e. Heat MgCO3

f. Silver Nitrate is added to solutions of1) NaBr2) NaCl3) NaIg. Potassium Bromide has Cl2 bubbled through it