Thursday, September 17, 2009 @ 5:16 AM Why does salt melt ice?.
done by Winnie and Tiffany (3z)
Definition:
Salt: a salt is made of cation which comes from the base and an anion which comes from the acid.
NaOH + HCl -> NaCl + H2O
salt can form acidic, neutral or alkaline solution
i) form neutral solution: sodium chloride dissolves in water
NaCl -> Na+ + Cl-
ii) form alkaline solution: sodium ethanoate dissolve in water, its solution is slightly alkaline. derived from a weak acid CH3COOH and a strong base NaOH
CH3COONa -> CH3COO- + Na+
iii) form acidic solution: ammonium chloride dissolves in water, its slightly acidic. NH4Cl is derived from a weak base NH3 and a strong acid HCl.
NH4Cl -> NH4+ + Cl-
Some interesting facts about salt
1/ if you try the heat test to salt, there is nothing happens except you may find tiny dents in aluminium foil.
2/ Only 6% of the salt used in the U.S. is used in food; another 17% is used for de-icing streets and highways in the winter months.
3/ Sodium Chloride is formed when the unstable metal sodium reacts with chlorine gas. It is the only family of rocks regularly eaten by humans.
4/ After aviation fuel is purified, salt is mixed with it to remove all traces of water before it can be used.
Topic: experiment with salt NaCl and ice
Aim:
to investigate the effect of table salt ( sodium chloride , NaCl) on melting ice an freezing ice
Introduction:
salt has many advantages. in real life, such as ice melting, control of human body fluids, storage foods in long term,etc. in this experiment, we are going to investigate how salt NaCl is able to melt ice.
it is because when ice and water are placed in contact:
Molecules on the surface of the ice escape into the water (melting)
molecules of water are captured on the surface of the ice (freezing)
1/ When the rate of freezing is the same as the rate of melting, the amount of ice and the amount of water won't change on average. The ice and water are said to be in equilibrium with each other. The balance between freezing and melting can be maintained at 0°C (the melting point of water) unless conditions change in a way that favors one of the processes over the other.
the equilibrium will be change when adding NaCl crystals to the experiment. Consider replacing some of the water molecules with NaCl. it dissolves in the water, but do not pack easily with molecules in the solid.So fewer water molecules present in a system.it leads to total number of waters captured by the ice goes down, so the rate of freezing decreases. The rate of melting is unchanged by the presence of NaCl, so melting occurs faster than freezing.
( temperature is constant at 0°C)
It is a reason why salt melts ice.
( can refer to the video on http://antoine.frostburg.edu/chem/senese/101/solutions/faq/why-salt-melts-ice.shtml )
2/ However, as more water melts, the NaCl is diluted, so it does not prevent the liquid water joining to the ice as effectively. Eventually the NaCl is diluted enough that some of the water can be captured by the ice again. Moreover, if the condition of temperature falls down below 0°C, water will change from a liquid to a solid. This change in composition makes it harder for water molecules to join together and form crystals. As a result, liquid water will be freeze.
It is why salt freezes ice.
Experiment:
apparatus and materials:
2 ice cube ~ 6 x 8 x 2 cm3
beaker x2
1 teaspoon of NaCl salt x 2
stop watch x 2
thread
ice container
thermometer
Procedure of ice melting by using salt
1/ putting 6 x 8 x 2 cm3 ice cube into a beaker in a ice container and using a thermometer to measure the temperature of the ice container at0°C
2/ putting a teaspoon of NaCl into the beaker
3/ using a stop watch to measure time until the ice is completely melting.
Procedure of ice freezing by using salt
1/ putting 6 x 8 x 2 cm3 ice cube into a beaker in a ice container and using a thermometer to measure the temperature of the ice container at0°C
2/ lay the thread on top of the ice in the beaker
3/putting a teaspoon of NaCl into the beaker around the thread
4/ using a stop watch to measure time until the ice starts to melt.
5/ putting more ice into ice container to control the temperature drops down below 0°C.
6/ waiting for about 2 mins
7/ slowly pull the ends of the thread up. find out that the ice has frozen to the thread.
Applications:
1/ Since salt prevents ice crystals forming in water, adding salt to water effectively lowers its freezing point. This is why the oceans don't freeze, even when the temperature is well below 0 °C.
In colder parts of the world, salt is often used on footpaths and roads to melt ice and snow.
When ice melts, it absorbs heat energy from its surroundings. When you add salt to ice, the rapid melting of the ice can cool the ice and water to below 0 °C. Before refrigeration was invented, ice and salt was used to produce the rapid cooling needed to make ice cream.
2/ Salt is also used to make homemade ice cream by melt the ice and keep it from refreezing so we can freeze the ice cream.
Thursday, September 17, 2009 @ 5:16 AM Why does salt melt ice?.
done by Winnie and Tiffany (3z)
Definition:
Salt: a salt is made of cation which comes from the base and an anion which comes from the acid.
NaOH + HCl -> NaCl + H2O
salt can form acidic, neutral or alkaline solution
i) form neutral solution: sodium chloride dissolves in water
NaCl -> Na+ + Cl-
ii) form alkaline solution: sodium ethanoate dissolve in water, its solution is slightly alkaline. derived from a weak acid CH3COOH and a strong base NaOH
CH3COONa -> CH3COO- + Na+
iii) form acidic solution: ammonium chloride dissolves in water, its slightly acidic. NH4Cl is derived from a weak base NH3 and a strong acid HCl.
NH4Cl -> NH4+ + Cl-
Some interesting facts about salt
1/ if you try the heat test to salt, there is nothing happens except you may find tiny dents in aluminium foil.
2/ Only 6% of the salt used in the U.S. is used in food; another 17% is used for de-icing streets and highways in the winter months.
3/ Sodium Chloride is formed when the unstable metal sodium reacts with chlorine gas. It is the only family of rocks regularly eaten by humans.
4/ After aviation fuel is purified, salt is mixed with it to remove all traces of water before it can be used.
Topic: experiment with salt NaCl and ice
Aim:
to investigate the effect of table salt ( sodium chloride , NaCl) on melting ice an freezing ice
Introduction:
salt has many advantages. in real life, such as ice melting, control of human body fluids, storage foods in long term,etc. in this experiment, we are going to investigate how salt NaCl is able to melt ice.
it is because when ice and water are placed in contact:
Molecules on the surface of the ice escape into the water (melting)
molecules of water are captured on the surface of the ice (freezing)
1/ When the rate of freezing is the same as the rate of melting, the amount of ice and the amount of water won't change on average. The ice and water are said to be in equilibrium with each other. The balance between freezing and melting can be maintained at 0°C (the melting point of water) unless conditions change in a way that favors one of the processes over the other.
the equilibrium will be change when adding NaCl crystals to the experiment. Consider replacing some of the water molecules with NaCl. it dissolves in the water, but do not pack easily with molecules in the solid.So fewer water molecules present in a system.it leads to total number of waters captured by the ice goes down, so the rate of freezing decreases. The rate of melting is unchanged by the presence of NaCl, so melting occurs faster than freezing.
( temperature is constant at 0°C)
It is a reason why salt melts ice.
( can refer to the video on http://antoine.frostburg.edu/chem/senese/101/solutions/faq/why-salt-melts-ice.shtml )
2/ However, as more water melts, the NaCl is diluted, so it does not prevent the liquid water joining to the ice as effectively. Eventually the NaCl is diluted enough that some of the water can be captured by the ice again. Moreover, if the condition of temperature falls down below 0°C, water will change from a liquid to a solid. This change in composition makes it harder for water molecules to join together and form crystals. As a result, liquid water will be freeze.
It is why salt freezes ice.
Experiment:
apparatus and materials:
2 ice cube ~ 6 x 8 x 2 cm3
beaker x2
1 teaspoon of NaCl salt x 2
stop watch x 2
thread
ice container
thermometer
Procedure of ice melting by using salt
1/ putting 6 x 8 x 2 cm3 ice cube into a beaker in a ice container and using a thermometer to measure the temperature of the ice container at0°C
2/ putting a teaspoon of NaCl into the beaker
3/ using a stop watch to measure time until the ice is completely melting.
Procedure of ice freezing by using salt
1/ putting 6 x 8 x 2 cm3 ice cube into a beaker in a ice container and using a thermometer to measure the temperature of the ice container at0°C
2/ lay the thread on top of the ice in the beaker
3/putting a teaspoon of NaCl into the beaker around the thread
4/ using a stop watch to measure time until the ice starts to melt.
5/ putting more ice into ice container to control the temperature drops down below 0°C.
6/ waiting for about 2 mins
7/ slowly pull the ends of the thread up. find out that the ice has frozen to the thread.
Applications:
1/ Since salt prevents ice crystals forming in water, adding salt to water effectively lowers its freezing point. This is why the oceans don't freeze, even when the temperature is well below 0 °C.
In colder parts of the world, salt is often used on footpaths and roads to melt ice and snow.
When ice melts, it absorbs heat energy from its surroundings. When you add salt to ice, the rapid melting of the ice can cool the ice and water to below 0 °C. Before refrigeration was invented, ice and salt was used to produce the rapid cooling needed to make ice cream.
2/ Salt is also used to make homemade ice cream by melt the ice and keep it from refreezing so we can freeze the ice cream.
