C4- calculations➖➕➗✖️
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RECAP: What’s an isotope?
Isotopes are: atoms of the same element, with a different number of neutrons.
What is the difference between relative formula mass and relative atomic mas? Hint: add all of the ________ atomic mass of each _______, in the compound.
• relative atomic mass is always the biggest number on the periodic table (when we look at an element). We don’t have to calculate anything. Think m, for massive. • However, with relative formula mass, you need to calculate it, using their periodic table. And by adding all of the relative atomic mass of each element, in the compound.
What is relative formula mass? Hint: adding
• With relative formula mass [Mr], you need to calculate it, using their periodic table. • And by adding all of the relative atomic mass of each element, in the compound.
What is relative atomic mass?
• relative atomic mass [Ar] is always the biggest number on the periodic table (when we look at an element). • We don’t have to calculate anything. Think m, for massive.
What’s the equation for percentage by mass equation? Hint: x no of _____ in that element.
• Ar of element in compound x no of atoms of that element/Mr of compound. • Then multiply by 100
RECAP: What’s the equation that links number of moles, mass and relative formula mass?
Number of moles= Mass _____________ Mr
What is Avogrado’s constant? And what’s it used for?
6.02x10^23 • Avogrado’s constant is used to calculate the no. of atoms or molecules.
Fill in the gaps: • When we use the number of _____ , mass and Mr equation we might have a single element, instead of a ________ • If this is the case, only use the relative ______ mass of that _______.
• When we use the number of moles, mass and Mr equation we might have a single element, instead of a compound. • If this is the case, only use the relative atomic mass of that element.
What is the conservation of mass? Hint: atoms
• mass is always conserved in a chemical reaction because: • In a chemical reaction, no atoms are created or destroyed. Only the bonds between atoms change.
What is the exception to the conservation of mass? Hint: might seem to change because… , float and come from Hint#2: scales take into account
• when a reaction involves a gas, the mass might seem to change because the gas can come from the air, or float of into the air. • [our scales might not also weigh all the reactants, because it didn’t take into account the gas]
In an equation, what side is the products and the reactants?
The reactants are on the left side + the products are on the right.
If an experiment was to be done in a sealed container, and measured. What will it take into account? Hint: the gas and
• Because the gas would be trapped in the container, when the reactants’ mass are measured, it would take into account: the gas and the solid.
Why might a mass seem to increase? Hint: reactants
• the mass may seem to increase because one of the reactants is a gas, that’s found in the air. • And all the products are: solids, liquids or aqueous.
Why might a mass seem to decrease?
• the mass may seem to decrease, because one of the products is a gas.
Referring to reaction vessels, explain why a mass may seem to increase. [3] Hint: floating, part of the product, inside
• before reaction, gas is floating around in the air and it is not contained in the reaction vessel- meaning you can’t account for its mass. • ; when the gas reacts to form, part of the product, it becomes contained inside the reaction vessel. • this means the total mass of the ‘stuff’ inside the reaction vessel increases.
Referring to reaction vessels, explain why a mass may seem to decrease. [4] Hint: before, isn’t enclosed, gas expands, no longer contained. Hint#2: can’t account for…
• Before a reaction, all the reactants are contained in the reaction vessel. • But if vessel isn’t enclosed, the gas can escape from the reaction vessel as it’s formed. • This is because a gas expands to fill a container it’s in, so if • it’s no longer contained in it’s reaction vessel, gas expands out from the vessel + escapes into air around——> means you can’t account for its mass + total mass of reaction vessel decreases, if it’s not sealed.