At pH 6.0 the N-terminus of His-His-His-His would have a (positive/ negative) charge. The C-terminus would have a (positive/ negative) charge. Since the pKa for His is 6.0, essentially half of the residues would carry a (negative/ positive) charge on their side chains, so that the charge per residue could be considered to be (+2.0/ +0.5 / +1.0/ +1.5). The result would be a net charge on the tetrapeptide of (+2.0/ -1.0/ +1.0/ -2.0). The tetrapeptide would be (more/ less) soluble in water than Histidine itself. When the bonds are formed between the carboxylate and amino groups to form the tetrapeptide, the groups that would interact with water are lost.

3.) for each of the following compounds, draw the major organic product of reaction with hcl or naoh and circle whether the starting materials and products will be more soluble in organic solvent or water benzoic acid + hcl: benzoic acid + naoh: oh benzoic acid water/organic water organic fluorenone hс: fluorenone + naoh: fluorenone water/organic water/organic веnzocaine + hci: benzocaine + n»oh: h2n benzocaine water/organic water organic o=

The scheme below is from a series of reactions that are part of a synthesis of vitamin a. answer the following questions with reference to this scheme. (i) what is "reagent a"? (ii) draw a step-by-step mechanism which explains the formation of compound c from compound b (iii) which reagents would you use to form compound e from compounds c and d (reagents b and c)? for each reagent suggested above in (ii) explain the role of the reagent in the reaction to (iv) form compound e. you may wish to do this by drawing a mechanism. 1. addition of reagent a но reagent a 2. н,о" thо oh нон-с compound a. compound b. compound c .ch-оh 1. reagent b "сно 2. reagent c сh oh compound e. compound d.

Agroup of students is studying convection current. they fill two identical balloons with the same amount of helium. one balloon is placed in a freezer and the other is in an area with warm air. after 10 minutes, the balloon are released from a height of 1 meter. which of the following to the students most likely observe? a) the warm balloon expands and rises. the cold balloon shrinks and sinks b) the balloon both rise. the cold balloon is larger than the warm balloon c) the cold balloon expands and rises. the warm balloon shrinks and sinks d) the balloon rise at the same rate. both balloons are the same size