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Question from Sharon
Question Number:	Q1
Topic/ Subject:
Solution X is an aqueous solution of 1.00 mol/dm3 sulphuric acid. Solution Y is an aqueous solution of 0.025 mol/dm3 sodium sulphate. A 25.0 cm3 portion of the acid solution X is diluted with the salt solution Y to a total final volume of 250 cm3. (i) Calculate the number of moles of acid present in the final solution. (ii) The pH of a solution is given by the formula pH = -log10(concentration of H+ in mol/dm3) Use this formula to calculate the pH of the final solution. (iii) Calculate the concentration of sulphate ions in the final solution

Question from Sharon
Question Number:	Q2
Topic/ Subject:
Black copper(II) oxide powder was contaminated with a small quantity of carbon powder. A student was asked to determine the percentage purity of 6.0g of the impure copper(II) oxide. The student decided to use an excess of 2.0 mol/dm3 sulphuric acid as it reacts with copper(II) oxide to form copper(II) sulphate solution and water, which can then be filtered leaving the undissolved carbon powder as the residue. (a) Write a balanced equation, including state symbols, for the reaction of sulphuric acid with copper(II) oxide as described above. After obtaining the copper(II) sulphate crystals, he weighed them and found the mass of copper(II) sulphate crystals obtained to be 10.8g. (b) Calculate the mass of copper(II) oxide that reacted with the dilute sulphuric acid. (c) What is the percentage purity of the copper(II) oxide? In a separate experiment, a student was given 250cm3 of the 5.0 mol/dm3 dilute sulphuric acid (d) How much distilled water must he add to the 250cm3 of dilute sulphuric acid in order to get the concentration of 2.0 mol/dm3? (e) Describe the observation when 50g of powdered lead(II) carbonate was added to 100cm3 of 2.0 mol/dm3 of dilute sulphuric acid.

Question from Grace Kwek
Question Number:	Q3
Topic/ Subject:	Secondary: Chemistry.
When and how to use 'Whom' and 'Who'? Thanks.