Formulae & Equations (Cambridge (CIE) IGCSE Combined Science: Chemistry): Flashcards
Exam code: 0653
1/200Still learning
Know0
- FrontFormulae
What is a molecular formula?
Was this flashcard helpful?
Cards in this collection (20)
What is a molecular formula?
A molecular formula shows the types of atoms in a molecule (given by chemical symbols) and the number of each type of atom (given by subscript numbers).
Seven elements exist as diatomic molecules, meaning each molecule contains .......... atoms of the same element.
Seven elements exist as diatomic molecules, meaning each molecule contains two atoms of the same element.
The seven diatomic elements are H2, N2, O2, F2, Cl2, Br2 and I2.
How many atoms of each element are present in sulfuric acid, H2SO4?
H2SO4 contains 2 hydrogen atoms, 1 sulfur atom and 4 oxygen atoms.
The subscript number after each symbol gives the count; where no subscript is shown, there is 1 atom.
True or False?
All seven diatomic elements are non-metals.
True.
The seven diatomic elements — hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine and iodine — are all non-metals.
What is an ionic compound?
An ionic compound is a compound formed when a metal reacts with a non-metal, producing positive metal ions and negative non-metal ions held together by electrostatic attraction.
What is the swap-and-drop method and when is it used to find an ionic formula? (Extended Tier Only)
The swap-and-drop method is used when two ions have different charges. The size of each ion's charge becomes the subscript of the other ion, giving the ratio that produces an overall neutral compound.
In an ionic compound, the overall charge is .......... because the positive charges on the cations are cancelled by the negative charges on the anions.
In an ionic compound, the overall charge is zero because the positive charges on the cations are cancelled by the negative charges on the anions.
What is the formula of copper(II) chloride, given that copper(II) ions are Cu2+ and chloride ions are Cl-? (Extended Tier Only)
The formula is CuCl2.
One Cu2+ ion requires two Cl- ions to cancel the overall charge, giving the ratio 1:2.
True or False?
The carbonate ion has the formula CO32-.
True.
The carbonate ion, CO32-, is a polyatomic ion carrying a 2– charge, made of one carbon atom bonded to three oxygen atoms.
Why must the swap-and-drop method give the simplest whole-number ratio when the two ions have the same charge? (Extended Tier Only)
After swapping and dropping, always simplify to the lowest whole-number ratio. If the method is applied without simplifying, it can produce incorrect formulas such as Ca2O2 instead of CaO. Equal charges give a 1:1 ratio — no further simplification is needed in that case.
What is a word equation?
A word equation shows the reactants and products of a chemical reaction written as full chemical names, with reactants on the left and products on the right of an arrow.
In a word equation, the substances on the left of the arrow are called .......... and the substances on the right are called ..........
In a word equation, the substances on the left of the arrow are called reactants and the substances on the right are called products.
Write the word equation for the reaction of ammonia with nitric acid.
Ammonia + nitric acid → ammonium nitrate.
Ammonia and nitric acid are the reactants; ammonium nitrate is the sole product.
What is a symbol equation?
A symbol equation uses chemical formulas to represent reactants and products, showing the relative numbers of each species and must be balanced so atom counts are equal on both sides.
True or False?
When balancing an equation, you can change the subscript numbers in a formula.
False.
You can only change the coefficients (numbers in front of formulas). Changing subscripts would alter the identity of the substance.
What are the four state symbols used in symbol equations and what does each represent?
The four state symbols are (s) for solid, (l) for liquid, (g) for gas and (aq) for aqueous (dissolved in water).
A symbol equation must be balanced so that the number of .......... of each element is the same on both sides of the arrow.
A symbol equation must be balanced so that the number of atoms of each element is the same on both sides of the arrow.
This reflects the law of conservation of mass.
Why is it useful to treat a polyatomic ion (e.g. NO3–) as a single unit when balancing an equation?
Treating an unchanged polyatomic ion as a single unit simplifies the balancing process. If the group appears on both sides of the equation unchanged, counting it as one entity avoids errors from counting individual atoms separately.
True or False?
Ionic equations must always include state symbols. (Extended Tier Only)
True.
State symbols are essential in ionic equations because they distinguish between species in solution (aq) and those that are solid, liquid or gaseous.
What are spectator ions and how are they identified in an ionic equation? (Extended Tier Only)
Spectator ions are ions that appear on both sides of a full ionic equation unchanged. They are removed from the ionic equation because they do not take part in the reaction.
Sign up to unlock flashcards
or