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2. Atoms, molecules and stoichiometry
A section of Chemistry, 9701
Listing 10 of 208 questions
A number of isomers with the formula Cr(H2O)6Cl 3 exist. Their general formula is [Cr(H2O)6-nCl n]Cl 3-n.nH2O. Each isomer contains a six co-ordinated Cr(ion in an octahedral complex. Water molecules not directly bonded with the Cr atom are held in the crystal lattice as water of crystallisation. The Cr–Cl bond is not easily broken and so chloride bonded with the Cr(ion in the complex does not react. 1.00 g samples of three of the isomers, A, B and C, were dissolved in separate samples of water. An excess of AgNO3was added to each and the mass of AgCl formed was measured. Ag++ Cl –AgCl The number of moles of AgCl formed was calculated. The table shows the results. isomer moles of AgCl formed from 1.00 g of isomer A 3.75 × 10–3 B 7.50 × 10–3 C 1.13 × 10–2 Calculate the Mr of Cr(H2O)6Cl 3. Mr Cr(H2O)6Cl 3 = Use the data in the table above to calculate the value of n for each of the isomers, A, B and C. Complete the table below with the values of n and the molecular formula of each isomer, in the style of the general formula given above. Show your working for at least one calculation of n. isomer n molecular formula A B C Two isomers have the same shape and their formula is Ni(R3P)2(CN)2, where R = CH3. Only one of these isomers has a dipole moment. Name the type of isomerism shown by Ni(R3P)2(CN)2. Draw structures of these two isomers. isomer 1 isomer 2 State which isomer has a dipole moment. Explain your answer.
9701_s17_qp_42
THEORY
2017
Paper 4, Variant 2
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Many naturally occurring esters are used as flavourings in food. The structure of ester V is shown. O O V Name V. V reacts with a reagent to form a salt of a carboxylic acid and an alcohol. Identify a reagent that could be used in this reaction. Draw the displayed formula of the alcohol made during this reaction.  State one other possible use for V, apart from as a food flavouring. Ester W is made up of 54.5% carbon, 9.1% hydrogen and 36.4% oxygen. Calculate the empirical formula of W.  State what additional information is required to determine the molecular formula of W. Compounds X, Y and Z are shown. They all have the same molecular formula. O O X OH O O O Y Z Deduce the molecular formula of X, Y and Z. In three experiments, sodium is added to separate samples of X, Y and Z. Complete the table to show the observations for each of these three experiments. Ignore any temperature changes which may occur. experiment observations Na + X Na + Y Na + Z  Sodium carbonate solution reacts with methanoic acid. Write the equation for this reaction. 
9701_s19_qp_22
THEORY
2019
Paper 2, Variant 2
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Separate samples of R, S, T and U are added to cold water. The identity of each sample is unknown. However, each sample is known to be pure and can only be one of Ba(OH)2, NaCl, P4O10 or SiCl 4. Use the observations in the table to identify each sample as one of Ba(OH)2, NaCl, P4O10 and SiCl 4. Write your answers in the table. state at room temperature observations on addition of sample to water identity of sample R solid alkaline, colourless solution is produced, some white solid remains S solid white solid disappears, solution is neutral T liquid misty fumes produced, white solid is made in vigorous reaction U solid acidic, colourless solution produced in vigorous reaction  Identify the formula of the white solid made when sampleT reacts with water. Name the solution formed when sampleU reacts with water. Magnesiumoxide and aluminiumoxide have properties typical of ceramic materials. Name one physical property typical of ceramic materials. Give the formula of another Period3 oxide which behaves as a ceramic material. Tungsten oxide, WxOy, is used to give colour to ceramic materials. A sample of WxOy contains 79.29% tungsten by mass. Calculate the empirical formula of WxOy. Show your working.  empirical formula =  
9701_s21_qp_23
THEORY
2021
Paper 2, Variant 3
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In 1814, Sir Humphrey Davy and Michael Faraday collected samples of a flammable gas, A, from the ground near Florence in Italy. They analysed A which they found to be a hydrocarbon. Further experiments were then carried out to determine the molecular formula of A. What is meant by the term molecular formula? Davy and Faraday deduced the formula of A by exploding it with an excess of oxygen and analysing the products of combustion. Complete and balance the following equation for the complete combustion of a hydrocarbon with the formula CxHy . CxHy + (x + y 4)O2 + When 10 cm3 of A was mixed at room temperature with 50 cm3 of oxygen (an excess) and exploded, 40 cm3 of gas remained after cooling the apparatus to room temperature and pressure. When this 40 cm3 of gas was shaken with an excess of aqueous potassium hydroxide, KOH, 30 cm3 of gas still remained. What is the identity of the 30 cm3 of gas that remained at the end of the experiment? The combustion of A produced a gas that reacted with the KOH. What is the identity of this gas? What volume of the gas you have identified in was produced by the combustion of A? cm3 What volume of oxygen was used up in the combustion of A? cm3 Use your equation in and your results from and to calculate the molecular formula of A. Show all of your working.
9701_w10_qp_21
THEORY
2010
Paper 2, Variant 1
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In 1814, Sir Humphrey Davy and Michael Faraday collected samples of a flammable gas, A, from the ground near Florence in Italy. They analysed A which they found to be a hydrocarbon. Further experiments were then carried out to determine the molecular formula of A. What is meant by the term molecular formula? Davy and Faraday deduced the formula of A by exploding it with an excess of oxygen and analysing the products of combustion. Complete and balance the following equation for the complete combustion of a hydrocarbon with the formula CxHy . CxHy + (x + y 4)O2 + When 10 cm3 of A was mixed at room temperature with 50 cm3 of oxygen (an excess) and exploded, 40 cm3 of gas remained after cooling the apparatus to room temperature and pressure. When this 40 cm3 of gas was shaken with an excess of aqueous potassium hydroxide, KOH, 30 cm3 of gas still remained. What is the identity of the 30 cm3 of gas that remained at the end of the experiment? The combustion of A produced a gas that reacted with the KOH. What is the identity of this gas? What volume of the gas you have identified in was produced by the combustion of A? cm3 What volume of oxygen was used up in the combustion of A? cm3 Use your equation in and your results from and to calculate the molecular formula of A. Show all of your working.
9701_w10_qp_22
THEORY
2010
Paper 2, Variant 2
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Questions Discovered
208