I'd like quick and simple answers to these chemistry questions please. Read on...?

Question

1. Liquids generally have lower density compared to their solid state. Then why does ice float on water?

2. Why does an air cooler cool better on a hot, dry day?

Please answer the above keeping in ming that my school follows the 9th standard CBSE portions and that I have a science exam tomorrow.

The answers to these two in the previous question didn't seem too clear.

Answer 1

I'm not sure about the CBSE, but I'll try explaining it anyway.

1.
Water is a pretty special substance because it expands upon freezing. (Which is why you can't freeze it in an enclosed bottle or it will crack.) This means that for the same mass, the volume is more.

Density = mass / volume, thus when your mass is constant and the volume increases, the density decreases. This is why ice floats on water, because water has a higher density than ice.


2.
First I'll explain the hot part. On a hot day, the temperature difference between the air and the desired temperature is much greater than on a cooler day. Generally, heat is transferred at a much higher rate if the temperature difference is great. Thus, the air cooler can cool the air quickly by since the heat can travel from the air to the coolant at a high rate.

Air has a lower specific heat capacity than water. This means to say that for the same mass of air and water, the air requires less energy to raise its temperature by 1K. It means that for the same amount of energy supplied, the air can be cooled/warmed faster than water.

On a dry day, there isn't as much water vapour as on a humid day, thus the air cools more quickly.

Answer 2

1. When water freezes the molecules get arranged in such a way that there are hollows formed between the hydrogen and oxygen molecules forming a honeycomb(beehive) structure. the presence of these hollows reduces the mass of the ice and increases its volume. As the volume becomes greater than the mass the density of the ice goes below 1 gm/cc which is less than the density of water and thus the ice floats on water although it is a solid.


2. On a hot day your body absorbs heat from the surroundings and gets heated. The cool air has less of heat and thus absorbs heat from your body making you feel better.


Best of Luck!

Answer 3

Water molecules are also attracted to each other by weaker chemical bonds (hydrogen bonds) between the positively-charged hydrogen atoms and the negatively-charged oxygen atoms of neighboring water molecules. As water cools below 4°C, the hydrogen bonds adjust to hold the negatively charged oxygen atoms apart. This produces a crystal lattice, which is commonly known as 'ice'.
Ice floats because it is about 9% less dense than liquid water. In other words, ice takes up about 9% more space than water, so a liter of ice weighs less than a liter water. The heavier water displaces the lighter ice, so ice floats to the top. One consequence of this is that lakes and rivers freeze from top to bottom, allowing fish to survive even when the surface of a lake has frozen over. If ice sank, the water would be displaced to the top and exposed to the colder temperature, forcing rivers and lakes to fill with ice and freeze solid.

Answer 4

1. Usually liquid is more denser than their solid state because:
A substance remain in liquid state the force of adherence between its molecules are lesser than the corresponding of solid state. Since there is a strong adherence force among it's molecules in the solid state the matter can occupy in less volume. If the same mas of the substance remains in the liquid state the force of adherence is less among its molecules and it occupy in a larger volume. Since the liquid state has a large volume it has a large density...
ICE is floating over watter because ice has a lesser density than the water its density are as follows
ICE: 0.917 g/cm³ at 0 °C
Water: 1.00 g/cm³, at 4 °C

Answer 5

Hi,

Why ice floats: You are right in the first part.. substances float when their density is less than other component in a liquid. Most solids are denser than liquids but ice is an exception. When water is frozen, it becomes solid (ice) and about 9% less dense. Click on this link to learn more:

http://chemistry.about.com/od/chemistryfaqs/f/icefloats.htm

Answer 6

a million?the hydrogen-bonds have somewhat to do with it. whilst water freezes and could become ice, they variety bonds between the molecules which motives some area to variety, making the ice crystal much less dense than different beverages formed into good states. 2. In a saucer, the portion of tea uncovered to kick back air is extra effective than in a cup, so for sure the liquid itself cools swifter, permitting us to drink it much less confusing. 3. warmth has an inclination to bypass from heat to chilly.(?) Water by itself in no way will become heat. you're able to have somekind of power rigidity to try this, and in any different case, it would merely get cooler until eventually at last it reaches a undeniable element (reckoning on surrounding temperature). i desire the authentic 3 helped. a minimum of thats what we study here in Japan (i think of/haha).

Answer 7

1. Due to enormous expansion theory ice floats on water. This is because water is more denser at 4 C due to this H atoms bonding with O atoms comes close together and hence water is denser and ice floats on water.

Answer 8

because the structure of ice is the form of a cage ..
due to which its volume increases so its relative
density compare to water decreases .
so it floats.

Answer 9

ya chem man is correct
1;hydrogen bonding
2;less humid