Question

When melting or boiling a substance (both of which are physical changes), which kinds of attractions may be broken? Circle all that apply. dipole-dipole London forces covalent bonds hydrogen bonding он но. Vs. If I told you that only one of these molecules is a solid at room temperature, which one is that more likely to be? How can you tell from the structure? Circle the hydrophilic portion of the molecules above and put a box around the hydrophobic parts. Are these molecules likely to dissolve in water? How have you decided? Identifying Chemical Reactions (2 pts) Name the organic reaction happening at each of the following steps in the Krebs cycle (pictured at right): Pynae Acetyi-CoA (a) succinate fumarate Calowceae Malat (b) fumarate malate Ketoglutan Succne SucdinyCo (c) malate oxaloacetate (d) isocitrate-a-ketoglutarate* (two rxns!!)

Answer 1

When a substance is either melted or boiled, the attraction that might break are hydrogen bonds, dipole-dipole interactions and london dispersion forces. These are weak forces and easily break by supplying little heat energy.

However covalent bonds are strong chemical bonds that do not easily break. Thus, when a substance is either melted or boiled, covalent bonds will not break.

Unsaturated fatty acids are liquid at room temperature. The structure on left is unsaturated fatty acid. It is a liquid at room temperature. It contains double bond in the hydrocarbon part.

C=0

Saturated fatty acids are solid at room temperature. The structure on right is saturated fatty acid. It is a solid at room temperature. It does not contains double bond in the hydrocarbon part.

C=0

OH oleic acid Unsaturated, liquid SOH stearic acid Saturated, solid

Hydrophilic parts are circled and hydrophobic parts are boxed as shown below.

OH oleic acid Unsaturated, liquid stearic acid Saturated, solid

Due to presence of large (non polar) hydrocarbon part, these molecules are not likely to dissolve in (poalr) water. This is because like dissolves like.

Step	Name of organic reaction
(a) succinate to fumarate	Dehydrogenation (A molecule of hydrogen is lost to form C=C double bond)
(b) fumarate to malate	Hydration (A water molecule is added to C=C double bond)
(c) malate to oxaloacetate	Oxidation (secondary alcohol is oxidised to ketone)
(d) isocitrate to alpha-ketoglutarate	(1) Oxidation (secondary alcohol is oxidised to ketone) (2) Decarboxylation (A molecule of carbon dioxide is eliminated)