我有幾題CHEM 的題目唔懂點做
希望大家可以幫下手
1) 1.2 g of a gaseous hydrocarbon Z are burnt competely in excess of dry oxygen in a suitable appartus , and the resultingb gas is led through concentrated sulphuric acid. The acid increases in mass by 1.86 g . Calculate the empirical formula of Z.
2.0 dm3 of Z, when measured at s.t.p. , weight 5.178g.Deduce the molecular formula of Z.
2) 1.200g of a compound containing only Carbon, Hydrogen and Oxygen gave on complete combustion 1.173g carbon dioxide and 0.24g water. Vapour density of the compound was 45. Find the empirical and molecular formula of the compound.
3)Complete combustion of 1.86g of an organic compund gave 2.64g of C02 and 1.62g of H20 as the only products.
If the density of the compound at s.t.p. was 2.77 g dm-3
, Find its molecular formula.
有埋STEPS 就最好LA THZ~~
chemistry queston
2011-02-09 11:59 pm
回答 (1)
2011-02-10 2:54 am
✔ 最佳答案
麻煩各位不要直接給答案; 只提供大約的方向和解法就夠了.2011-02-09 18:54:59 補充：
1.
CxHy + (x + y/4)O2 ------> xCO2 + (y/2) H2O
conc. sulph. absorbs water.
the increase in mass is due to absorption of water in the combustion product.
from the mass of water, calculate the no. of mole and, thus mass, of hydrogen present.
because all hydrogen in water comes from the hydrocarbon, mass and no. of mole of H in the HC can be determined.
mass of C in HC = total mass of HC - mass of H
then calculate no. of mole of C present.
you get no. of mole of H and C, then the empirical formula...
let the no. of carbon in this HC = a,
then molar mass = a x (molar mass of the empirical formula)
then, calculate no. of mole of Z in 5.178g.
then, use ideal gas equation to calculate actual no. of mole of Z.
compare to values, you'll eventually get a.
2.
you have to know the definition of vapor density.
what is it compared to? air? hydrogen gas? (probably hydrogen)
then, you'll know molar mass of the gas.
similar to Q.1, mass of C and H in the compound is calculated from mass of CO2 and H2O produced.
mass of O = total mass - mass of C - mass of H
then, calculate no. of mole of each element, get to know its empirical formula.
from empirical formula and molar mass, molecular formula is easy to get.
3.
using ideal gas law, find no. of mole of compound when the volume = dm^3 ;
with no. of mole and mass, you get molar mass.
empirical formula is determined similar to Q.1.
empirical formula + molar mass ------> molecular formula.
收錄日期: 2021-04-20 00:01:57
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20110209000051KK00976