Chemical Calculations

Descripción

A summary of the chemical calculation topics - in particular with regards to moles
Kate Blowers
Test por Kate Blowers, actualizado hace más de 1 año
Kate Blowers
Creado por Kate Blowers hace más de 7 años
143
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Resumen del Recurso

Pregunta 1

Pregunta
What is the correct equation for working out the percentage mass of an element in a compound?
Respuesta
  • (Relative formula mass x number of atoms of that element)/relative atomic mass of compound
  • (Relative atomic mass x number of atoms of that element)/relative formula mass of compound
  • (Relative atomic mass x relative formula mass of compoun)/number of atoms of that element

Pregunta 2

Pregunta
A mole is a system chemists use to count huge quantities of [blank_start]atoms or molecules[blank_end]. It is given the symbol [blank_start]n[blank_end], and is measured in a unit called the mole, shorthand [blank_start]mol[blank_end]. A mole of any substance contains the same number of atoms that are contained in [blank_start]12[blank_end]g of the isotope [blank_start]carbon-12[blank_end]. One mole of a substance is simply the [blank_start]relative atomic mass[blank_end] or [blank_start]formula mass[blank_end] expressed in [blank_start]grams.[blank_end]
Respuesta
  • atoms or molecules
  • n
  • mol
  • 12
  • carbon-12
  • relative atomic mass
  • formula mass
  • grams.

Pregunta 3

Pregunta
The reactant that gets used up first in a reaction is called the limiting reactant
Respuesta
  • True
  • False

Pregunta 4

Pregunta
Which of these do you need to work out the limiting reactant?
Respuesta
  • A balanced symbol equation
  • The relative formula mass
  • The number of moles of each reactant
  • The number of electrons

Pregunta 5

Pregunta
Percentage yield is the amount of a produce you [blank_start]actually make[blank_end] as a [blank_start]percentage of the amount[blank_end] you should [blank_start]theoretically make.[blank_end]
Respuesta
  • actually make
  • percentage of the amount
  • theoretically make

Pregunta 6

Pregunta
Why does a high percentage yield matter to people in the industry?
Respuesta
  • If a yield is know for a particular product you can work out how much reactant is needed
  • A higher percentage yield = less product to produce more = higher profit
  • It's easier to work out information
  • Raw materials are scarce and expensive and so must be carefully conserved

Pregunta 7

Pregunta
What is the correction equation for working out percentage yield?
Respuesta
  • Percentage yield = (Theoretical yield/actual yield) x 100
  • Percentage yield = (Number of atoms/theoretical yield) x 100
  • Percentage yield = (Actual yield/theoretical yield) x 100

Pregunta 8

Pregunta
Very few reactants have a percentage yield of 100% because:
Respuesta
  • Products may be left behind in the apparatus
  • It violates the law of conservation of mass
  • The reaction may not have completely finished
  • The raw minerals may not be pure
  • The atoms are destroyed in the reaction
  • Some reactants may give unexpected products
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