How does molarity relate to concentration? For sodium chloride (NaCl) they are in a ratio of 1:1 so the molar mass of NaCl is 22.99 + 35.45 = 58.44 g/mol.įor a compound like water (H 2O), 1 mole of hydrogen (H) is 1.008 g/mol and 1 mole of oxygen (O) is 15.9994 g/mol. One mole of sodium (Na) is 22.99 g, and 1 mole of chlorine is 35.45 g. The molar mass is the mass in grams of 1 mole of a particular molecule. So, 1 mole of hydrogen gas (H 2) contains 6.02x10 23 molecules, and 1 mole of glucose (C 6H 12O 6.) also contains 6.02x10 23 molecules, but as H 2 is a much simpler molecule, 1 mole of H 2 will have a much smaller mass (the molar mass) than 1 mole of C 6H 12O 6. This equates to roughly 6.02x10 23, also referred to as Avogadro's Number. A 1 M solution is said to be “one molar”.Ī mole is the quantity of anything that has the same number of particles as 12 g of carbon-12. An eccentric chemist weighed a piece of paper, wrote his name on it, and re-weighed it.Molarity is the concentration of a solution in terms of the number of moles of the solute in 1 dm 3 (1 liter) of the solution. Calculate the mass of the residue when 57.2 g of washing soda is completely dehydrated.ģ. (c) On heating, the washing soda crystals lose all the water present. (b) Calculate the relative formula mass of washing soda Na2CO3.10H2O (a) State what is meant by relative atomic mass. (c) Sketch the mass spectrum (not to scale) of naturally occurring uranium. Use the values to calculate the relative atomic mass of uranium to two decimal places. (b) The natural abundance of the two isotopes of uranium is: (a) Explain why 235 92U and 238 92U are regarded as isotopes of uranium. Given that cystine contains two sulphur atoms, what is the molar mass of cystine? Show your working clearly.ġ.
The sulphur content of cystine is 26.7 %. Calculate the value of x in the formula if 1.45 g of plaster of Paris is heated to dryness and 1.36 g of CaSO4 remains.Ĥ.
The calcium sulphate precipitated can be hydrated to make plaster of Paris, CaSO4.xH2O. Calcium oxalate may be converted to oxalic acid and calcium sulphate by reaction with dilute sulphuric acid: The mineral beryl, Be3Al2Si6O16, is the main source of beryllium.Ĭalculate the percentage, by mass, of beryllium in beryl.ģ. It is a steel-grey metal, which is extremely light. Beryllium occurs to a small extent in the earth's crust. Calculate the mass of the residue when 57.2 g of washing soda is completely dehydrated.Ģ. (ii) On heating, the washing soda loses all the water present. (b) (i) Calculate the relative formula mass of washing soda Na 2CO3.10H20 What is the empirical formula for this substance?ġ. Chemical analysis showed that a sample of a substance contained only carbon, hydrogen and nitrogen in the following amounts: carbon, 0.060 g hydrogen, 0.025 g and nitrogen, 0.070 g. If L is the Avogadro constant the number of ions in 17.43 g of solid K2SO4 (relative molecular mass 174.3) will beĩ. Calculate the number of protons present in the nuclei of the atoms contained in 2.24 dm3 of oxygen gas, O2, (atomic number of oxygen is 8) at standard temperature and pressure, given that one mole of gas under these conditions occupies 22.4 dm3 and the value of the Avogadro constant L = 6.0 x 1023 mol-1.Ĩ. The mole fraction of sulphur trioxide will beħ. Equal masses of sulphur dioxide and sulphur trioxide are mixed. Which one of the following is the percentage of sulphate in the unknown?Ħ.
0.0640 g of an unknown sulphate yielded 0.1165 g of barium sulphate when appropriately treated with barium chloride. What mass of iron(II) ammonium sulphate-6-water,Fe(NH4)2(SO4)3.6H2O, (relative molecular mass = 392) must be dissolved in water to produce 1 litre of a solution which is 0.05M with respect to Fe2+(aq)?ĥ. which one of the following is the percentage yield of the reaction Ĥ. If 8.2 g of sodium ethanoate produced 560 cm3 of methane (at s.t.p.). sodium ethanoate decomposes in accordance with the following equation.ĬH3COONa (s) + NaOH (s) CH4 (g) + Na2 CO3 (s) If 8.7 g of potassium sulphate is dissolved in water and made up to 200 cm3, what is the concentration of the solution in mol dm-3?ģ. Which one of the following equations correctly represents this reaction?Ģ. Iodate ions in the presence of acid oxidise sulphite ions to sulphate ions.
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