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Hydrogen Bonds!
The two helixes in DNA are held together by hydrogen bonds.
The water molecules in ice are held in place by hydrogen bonds
Three questions:
water expands when it freezes and ice therefore floats
1. Why is water a liquid and not a gas ( between 0 and 100oC) ?
Water has a Relative Molecular mass ( Mr) of 18 ... Oxygen's Mr is 32. If Mr was the only factor that affects the state of a substance then wouldn't you expect water to be a gas ?
2. Why does Ice float on water?
Most liquids become more dense as they cool. This causes them to freeze from the bottom up. However, water freezes from the top down. Ice cubes float on top of your drink. Ice is less dense than liquid water. How do we explain this?
3. How does a DNA molecule unzip?
DNA molecules can unzip themselves - separating the two strands of the double helix from each other. The individual strands themselves do not break and can then be replicated. What sort of bonding enables this to happen?
One answer:
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