CORE Chemistry (Short Course) - 9222 OxfordAQA

Use Of Amount Of Substance In Relation To Masses Of Pure Substances

Muhtasari

Two sacks stand side by side in a farm supply store. They hold the same mass, they cost the same money, and both are sold as nitrogen fertiliser. One of them will put more than twice as much nitrogen into the soil as the other, and nothing on the outside of either sack tells you which. The only way to find out is to read the chemical formula and do about ninety seconds of arithmetic. That arithmetic is what this lesson is about, and it is the single most useful piece of number work in the whole of chemistry.

You will start by learning to add up a formula, turning a string of symbols and subscripts into one number that stands for the mass of the whole unit. From there you will work out what fraction of a compound is the element you actually care about, which is how a farmer chooses between two sacks and how a mining company decides whether an ore is worth digging out of the ground. Then you will take that fraction off the page and put it to work on a real mass, turning a percentage into tonnes of metal or kilograms of nutrient. Three steps, one balance, and no instrument more exotic than a calculator.

Malengo

The relative formula mass (Mr) of a compound is the sum of the relative atomic masses of the atoms in the numbers shown in the formula. Students are expected to use relative atomic masses in the calculations specified in the subject content. Students should be able to calculate the relative formula mass (Mr) of a compound from its formula.
The percentage by mass of an element in a compound can be calculated from the relative atomic mass of the element in the formula and the relative formula mass of the compound.

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Maelezo ya Somo

A chemical formula looks like a label and behaves like an account book. Written out, NH4NO3 names a substance; read properly, it tells you exactly how the mass of that substance is shared out between nitrogen, hydrogen and oxygen, down to the last percent. Nothing else is needed to extract that information. No instrument, no experiment, no reference book beyond a periodic table. The formula already contains the answer and the arithmetic simply reads it out.

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Tathmini ya Somo

Hongera kwa kukamilisha somo la Use Of Amount Of Substance In Relation To Masses Of Pure Substances. Sasa kwa kuwa umechunguza dhana na mawazo muhimu, ni wakati wa kuweka ujuzi wako kwa mtihani. Sehemu hii inatoa mazoezi mbalimbali maswali yaliyoundwa ili kuimarisha uelewaji wako na kukusaidia kupima ufahamu wako wa nyenzo.

Utakutana na mchanganyiko wa aina mbalimbali za maswali, ikiwemo maswali ya kuchagua jibu sahihi, maswali ya majibu mafupi, na maswali ya insha. Kila swali limebuniwa kwa umakini ili kupima vipengele tofauti vya maarifa yako na ujuzi wa kufikiri kwa makini.

Tumia sehemu hii ya tathmini kama fursa ya kuimarisha uelewa wako wa mada na kubaini maeneo yoyote ambapo unaweza kuhitaji kusoma zaidi. Usikatishwe tamaa na changamoto zozote utakazokutana nazo; badala yake, zitazame kama fursa za kukua na kuboresha.

What is the relative formula mass of calcium carbonate, CaCO3? Relative atomic masses: C = 12, O = 16, Ca = 40. A. 68 B. 88 C. 100 D. 116 Answer: C
What is the percentage by mass of oxygen in water, H2O? Relative atomic masses: H = 1, O = 16. A. 11.1 B. 16.0 C. 50.0 D. 88.9 Answer: D
What is the relative formula mass of aluminium sulfate, Al2(SO4)3? Relative atomic masses: O = 16, Al = 27, S = 32. A. 123 B. 150 C. 278 D. 342 Answer: D
What is the percentage by mass of sulfur in sulfur dioxide, SO2? Relative atomic masses: O = 16, S = 32. A. 20.0 B. 33.3 C. 50.0 D. 66.7 Answer: C
A farmer spreads 30 kg of urea, CO(NH2)2, on a field. What mass of nitrogen does this supply? Relative atomic masses: H = 1, C = 12, N = 14, O = 16. A. 7.0 kg B. 12.5 kg C. 14.0 kg D. 28.0 kg Answer: C

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Vitabu Vinavyopendekezwa

OxfordAQA International GCSE Chemistry (9202)

Manukuu: Student Book

Mchapishaji: Oxford University Press

Mwaka: 2016

ISBN: 978-0-19-837589-0

Maelezo: The endorsed student book for the 9202 specification, covering the full subject content with required practicals and exam guidance.

OxfordAQA International GCSE Combined Sciences Chemistry (9204)

Manukuu: Student Book

Mchapishaji: Oxford University Press

Mwaka: 2017

ISBN: 978-0-19-842308-9

Maelezo: The chemistry half of the Combined Science series. A lighter parallel treatment of the same content, useful for a second explanation.

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