Part 3 Floating Or Sinking Flashcards
What decides on whether an object will float or sink?
The density of the object and the density of the water
If an object floats is the density higher or lower than the water?
Lower
If an object sinks is the density higher or lower than the water?
Higher
How is density calculated?
By dividing mass (kg) by volume (m)
Density kgm-3
What is the mass of 1 litre?
1 kg
Volumes of liquid are generally measured in litres although the litre is not a basic SI unit. 1 litre is equivalent to 0.001 m3 (cubed)
There are 1000 litres in 1 m3
Arrange the following elements in increasing order by mass starting with the lowest mass?
Chlorine, hydrogen, sodium, oxygen
Hydrogen, oxygen, sodium, chlorine
What elements are salt made of ?
Sodium and chlorine
How do you calculate the percentage of an object submerged in a liquid?
Divide the density of the object by the density of the liquid and convert to a percentage by multiplying by 100
What is the density of ice?
917 kg/m3 (cubed)
What is the density of water?
1000 kg/m3 (cubed)
What is the density of seawater?
1030 kg/m3 (cubed)
If the sodium atom loses an electron, how many protons and electrons are left, and what is the overall electrical charge?
The sodium electrons has 11 protons (12 neutrons) and its nucleus, which is surrounded by 11 electrons
In losing one electron the sodium atom reduces its number of electrons from 11 to 10, but the number of protons in the nucleus stays unchanged. The overall charge on what is left is therefore (+11-10 = +1) as there is one more proton that there are electrons
What is an ion?
It is the entity that remains after electrons are lost from (or gained by) an atom
E.g. Sodium ion is written Na+
This is because it loses an electron to the chlorine atom and therefore becomes more positively charged
How would you write the ion derived from chlorine, in which the chlorine gains one electron?
By analogy with the sodium ion, the chloride ion is written Cl-. Note the different term - a chlorine atom becomes a chloride ion in this case
What is ionic bonding?
It is the attraction of two opposite electrical charges and it is responsible for holding them together.
E.g. The sodium ion loses an electron to Chlorine atom - this makes sodium negatively charged and the chlorine atom more positively charge this holds them together
Are sodium chloride molecules held together by covalent bonding or ionic bonding and why?
Ionic bonding
Because the sodium loses an electron to the chloride therefore making them positively and negatively charged and therefore making them attract each other
How are the molecules arranged in solid NaCl?
They are regularly shaped grains known as crystals.
The ions themselves are arranged in a cubic array. They are held together by strong forces
What colour spheres represent sodium ions?
Smaller silver grey shapes spheres represent sodium
Which spheres represent chloride ions?
Larger green spheres
What is a solution?
A liquid with another substance dissolved in it - so that it has become part of the liquid
Solute dissolved in a solvent
What is a solute?
It is a substance that dissolves in a liquid
What is a solvent?
A liquid/gas that a substance can dissolve in
Is water a solute or solvent?
It is a solvent and is also called the universal solvent
Is water a polar or non polar solvent?
Water is a polar solvent because water molecules have a slight separation of electrical charge within the molecule
Can you think of any compounds that do not dissolve in water?
Oil does not dissolve in water
Why does oil float on water?
Because it is less dense
What does immiscible mean?
Incapable of mixing
Can polar solvents mixed with non polar solute? Or vice versa?
Polar substances prefer to dissolve in polar solvents and the same with non polar
What is another name for sugar?
Sucrose
Which atoms is the compound sucrose (sugar) molecule made from?
Carbon (C)
Hydrogen (H)
Oxygen (O)
How many atoms of carbon, oxygen and hydrogen are there in a molecule of sucrose?
There are
12 carbon atoms
22 hydrogen atoms
11 oxygen atoms
What is the chemical formula for sucrose?
C12H22O11
Is sucrose bonded by ionic bonding or covalent bonding?
Covalent bonding
Do you think sucrose is a polar molecule?
Sucrose is a polar molecule. Where the oxygen atoms have a slight negative charge and hydrogen atoms have a slight positive charge. Oxygen and hydrogen do not share electrons equally and the bonding between them is known as polar bonding. To create a polar molecule the polar bonds should collectively produce a separation of charge or polarisation. The sucrose molecule is not symmetric so the polar bonds are not balance across the molecule and hence there is some separation of charge
Explain why sucrose dissolves in water?
Polar water molecules attract negative/positive areas of the sucrose molecule making the sucrose molecules separate from each other and dissolve in water
Water and sucrose is a chemical reaction
How does salt dissolve in water?
The positive part of the water molecule surround the negative chloride ions and shepherd it off in to the surrounding water molecules.
The negative part of the water molecules surround the positive sodium ion and shepherd it off in to the surrounding water molecules
Does the solubility of sodium chloride change with temperature?
No it doesn’t
What is the most important variable that can affect the solubility of a substance?
Temperature
In general an increase in temperature tends to allow a greater mass of a substance to be dissolved in water e.g. Sugar in hot water
Define the term solubility?
The quantity of a particular substance that can dissolve in a particular solvent
When sodium chloride dissolves in water, If hydrogen bonds are weaker than the attraction between two ion crystals how does it break it up?
The strong attractive forces between ions have to be replaced by other equally strong forces hydrogen bonds are weaker than the attraction between two ions in a crystal structure, but many hydrogen bonds together exert a considerable force which can exceed the strength of the ionic attraction.
Apart from water what happens to the density of most liquids when the temperature increases?
The density decreases
What happens to the density of water up to 4 degrees Celsius?
The density increases
What happens to the density of water after 4 degrees Celsius?
After 4 degrees water behaves like other liquids
As the temperature increases the density decreases
Why does the density decrease when liquid increases its temperature?
Heating liquid water above 4 degrees causes molecules to speed up and spread slightly apart, occupying a larger volume. This will result in a decrease of its density
What happens to water molecules in a glass of water when you cool it down to 4 degrees Celsius?
The water molecules will slow down and get closer together occupying a smaller volume
At what temperature does water reach its maximum density?
4 degrees Celsius
If ice did not float what implications would this have on ponds and lakes?
They would freeze from the bottom up
As a result this would kill all fish and plants
In the warmer weather the uppermost part of the ice would melt first
This would stop the warmer air reaching the ice below and would inhibit melting at the bottom
What benefit does flowing ice have to ponds and lakes?
It absorbs and reflects sunlight and allows rapid thawing
It slows down the rate at which more ice can form
Define the term density
It is the mass of a substance that occupies one cubic metre
What is the SI unit of density?
kg/m³
Are ionic materials soluble or insoluble in water?
Soluble
What is ionic bonding responsible for?
Holding together two opposite electrically charge ions
