Topic 1 - Principles in Chemistry Flashcards
(54 cards)
How is a substance classified as an:
1. Element
2. Compound
3. Mixture
- A pure substance that consists of only one type of atom
- Two or more different elements that are chemically bonded together
- Two or more different elements, not chemically bonded together
Will a pure substance’s melting/boiling point be fixed, or a range of temperatures? Why?
The melting and boiling points of a pure substance will be fixed because it is pure, and all particles of the substance have the same properties and will change state at the same temperature.
Will a mixture’s melting/boiling point be fixed, or a range of temperatures? Why?
A mixture’s boiling point will be over a range of temperatures. This is because the mixture consists of different types of particles, which will have different properties and therefore different melting/boiling points. This means it will melt over a range of temperatures as the different parts will begin melting at different points.
What experiment would you do to separate a solvent from the solute when you want the solvent (e.g. getting water from salt water)? How would you do this?
You would use Simple distillation
E.G. Salt and Water
The solution is put in a flask and heated, as the water evaporates before the salt, the water rises in the flask and into a leibig condenser. The Leibig condenser has cool water flowing through it, which cools the evaporated water, and the condensed water then runs into a collecting flask.
What experiment would you use when you want a specific liquid from a mixture, when they have two different boiling points that are close? E.g. separating the water from cola or petrol from crude oil.
How would you do this?
You would use fractional distillation
E.G. Cola
Put the mixture in a flask and heat to a specific temperature. The water has the lowest boiling point, and so will evaporate first, leaving the flavouring and syrup etc behind. However, as the other ingredients have similar boiling points, the water will rise through a fractionating column, which has a spiral to slow down the rate of rise. As they reach the top, the column is cooler, so any other evaporating ingredients that evaporated early will condense and run back down into the flask. The water then goes through a Liebig condenser, where it condenses and runs into a collecting flask.
What process would you use to obtain the liquid in a mixture which contains a solid not dissolved in a liquid? E.g. Sand and water
How would you do this?
You would use filtration
E.g. Sand and water
The mixture is poured into a filter funnel above a beaker. Filter paper is placed in the funnel. The mixture is poured in, and the small holes of the filter funnel allow water through, but the sand can’t fit through, and so remains as a residue.
What method would you use to obtain solid crystals from a solution?
How would you do this?
You would use crystallisation
An impure solid dissolved in a solvent will be heated to evaporate most of the solvent. The solution will cool, and solid crystals will appear at the bottom of the solution. The cold solution is then poured off to get the crystals, which you can dry using filter paper.
What method would you use to separate a mixture of soluble substances and find what they are made of (e.g. different inks/dyes)?
How would you do this?
You would use paper chromatography
The inks/dyes are placed on a dotted pencil line on paper, sitting above solvent, while the bottom of the paper touches the solvent. The solvent will spread up the paper, and take the inks/dyes with it, showing the different colours.
How does a chromatogram provide information about the composition of a mixture?
It provides information as it shows the different components.
If it shows up as just one dot of colour and no other colours, it is a pure substance. If it has two or more colours, it is a mixture.
It can also be used to identify substances, and also make more of substances/quatify them as you know their components.
What is an Rf value? How can it be calculated? How can it be used to identify a component of a mixture?
An Rf value (retention factor) is how far a substance travels relative to a solvent. It is calculated by dividing the distance travelled by the substance by the distance travelled by the solvent. It can identify a substance because by comparing it’s Rf value to other known substances, it can help identify the substance because the Rf value is always the same in the same solvent.
What is an:
1. Atom
2. Molecule
- An atom is the smallest part of an element, consisting of a nucleus and electrons
- A molecule is two or more atoms chemically bonded together.
In an atom, where are the protons, neutrons and electrons’ positions? What are their masses and charges?
Protons and Neutrons are held in the nucleus. The electrons and held in electron shells surrounding the nucleus.
Proton - Mass 1, Charge +1
Neutron - Mass 1, Charge 0
Electron - Mass 1/1836, Charge -1
What is an:
1. Atomic number
2. Mass number
- The atomic number is the number of protons in an element (and coincidentally the number of electrons too). It identifies the element and is below the symbol on the periodic table
- The mass number is the number of protons and neutrons in an element, which is above the symbol on a periodic table
What is an isotope? What is relative atomic mass (Ar)?
An isotope is atoms of the same element with the same number of protons (Atomic Number) but a different number of neutrons (Mass Number)
Relative atomic mass is the mean mass of the different isotopes of an element.
How do you calculate Relative Atomic Mass (Ar)
Add up all the different isotopes’ mass numbers, and then divide by the total number of isotopes/total percentage of isotopes.
How are elements arranged in the periodic table?
In order of atomic number, in groups and periods depending on the number of electrons in the outer shell and the number of shells.
What are the limits of electrons in each shell for the first 20 elements? How would you draw them?
2,8,8,2
How would you use the electrical conductivity and acid-base character of oxides to classify an element as a metal or non-metal
If it conducts, it is a metal (or graphite)
If its oxide is basic, and reacts with acids to form salt and water, it is a metal
If its oxide is acidic or neutral, and it doesn’t conduct, it is a non-metal
Where on the periodic table is the divide between metals and non-metals?
Above Aluminum, below Boron, it then staircases down.
Why do elements in the same group have similar chemical properties?
They have the same number of electrons in their outer shell, and so will react similarly because they need to gain/lose the same number of electrons.
Why do the noble gases (Group 0) not react?
They don’t need to gain/lose electrons to gain a full outer shell, as they already have one, so there is no need to react to gain/lose electrons.
How do you calculate relative molecular mass/relative formula mass?
Add up all the atomic masses of all the atoms present in the molecule’s formula
What is the formula for moles, what are the units and rearrangements?
n = m / Mr
m = n x Mr
Mr = m / n
n = Number of moles (mol)
m = Mass (g)
Mr = Molecular Mass
How do you calculate percentage yield?
Actual yield / Theoretical yield
