2007 ADA Sample Test Questions

[hova137]

Advertisement - Members don't see this ad

51. During a titration it was determined that 30ml of a 0.1M Ce^4+ solution was required to react completely with 20ml of a 0.15M Fe^2+ solution. How do I find the reaction equation?

Also, I have heard the hole punching is not to scale on the real DAT...can anyone give me further explanation as to what this means?? Does it not look like the 2007 sample test and if not is it hard to figure out where they made the hole punch?

 

[Spartan812]

Ok, well A just doesn't make sense. I mean, there's no reason for water to be in the equation.

Next, think about what you're given. You're titrating ions together, so what's most likely to happen? A redox reaction. Since Ce has a more positive charge than Fe, it will be the one undergoing reduction. So basically, what we want is a charge balance!

Looking at answers B & E, we see that the oxidation number of iron is changing from 2 to 4. This means that iron is getting rid of 2e- at once. Well that can't be right. Think about it, iron is in an ionic state and is holding onto those electrons VERY tightly. It isn't going to give away 2e- at once willingly. So we can disregard B&E

Now let's look at D. Looking at the reaction, we see that the oxidation number of iron is being reduced by one, meaning that iron is losing 1e-, which makes sense. What doesn't make sense is the balanced equation, where Ce and Fe are in a 1:2 ratio and Ce is gaining 2e-.

Really the only one that makes sense is C, where for every e- that Fe is losing, Ce is gaining an e-. It is, in the end, the simplest reaction being presented.

Hope this all makes sense! 🙂

 

[hova137]

haha wow look at that reasoning power...thanks for the help...makes sense!

 

[shiftypoptart]

well you get molarity and volume therefore you can get mols of everything used. If you get the mols for both of the reactants you get one mol of each. The only reaction that has 1 mol for each of them is C.

 

[rwalk002]

Can someone please help with the following QR questions? I am stuck.

12. Which is the equation of the line that contains the point (3, -1) and is perpendicular to the line y = 3x + 3?

The answer is y = (-1/3)x but I don't understand how to get the answer.

33. For all y, the cos y is equal to

answer is cos(-y), is there basic info I need to memorize?

Pleas explain!

 

[Kahr]

Can someone please help with the following QR questions? I am stuck.

12. Which is the equation of the line that contains the point (3, -1) and is perpendicular to the line y = 3x + 3?

The answer is y = (-1/3)x but I don't understand how to get the answer.

I'm kind of at a loss as well, but through some deductive reasoning I thought I could find the answer. My first instinct, not knowing exactly what to do, was to plug in the point they give you (3, -1) and see if it works out in any of the answers. Awesomely enough, it only works for choice B (y=3x - 10), and E (y = (-1/3)x), so you've already narrowed the equation to those two answers. My second clue was that we know for two reasons that the slope of our answer line must be negative: the slope for our given line is positive and our answer has to be perpendicular to it, and even better, our given point has a negative slope because it contains one positive and one negative coordinate, whereas if both are positive or negative we have a positive slope. Looking at our left over answers, B and E, only E has a negative slope.

Sorry if that's not a super mathematical answer, I just worked the problem based on some guesswork, maybe it helps. 😳

33. For all y, the cos y is equal to

answer is cos(-y), is there basic info I need to memorize?

Pleas explain!
Sorry, I haven't gotten through trigonometry review yet, so I can't help you here, though I am certain you need to know the basic trig functions, of which cos() is one. Hopefully someone can explain here, lots of math wizards on this forum.

Cheers

 

[Dew517]

Can someone please help with the following QR questions? I am stuck.

12. Which is the equation of the line that contains the point (3, -1) and is perpendicular to the line y = 3x + 3?

The answer is y = (-1/3)x but I don't understand how to get the answer.

33. For all y, the cos y is equal to

answer is cos(-y), is there basic info I need to memorize?

Pleas explain!

For #12, the slope of a line perpendicular to another is the negative multiplicative inverse - if the slope is A the slope of the perpendicular line is always -1/A. So the slope must be -1/3. That answer has the correct slope and works out when you plug in the given point, so it must be right.

33. Cos is an even function, meaning if you plug in a positive number A or negative number -A the result will be the same. IN math terms, cos(a) = cos(-a). Sin is an odd function and will display a similar behavior:
sin(-a) = -sin(a). Meaning if you plug in a negative number -B you will get the negative result of plugging in the positive number B. You should memorize both of these properties and learn to recognize them.

 

[tkuhug]

Can someone explain #33 further or give an example of it?

For example is it saying cos 30 = cos -30 since cos-30 will be in the C quadrant, meaning it will be positive whereas cos positive 30 will be in A quadrant meaning all are positive? And similar reasoning applied to sin?

 

[FeralisExtremum]

Can someone explain #33 further or give an example of it?

For example is it saying cos 30 = cos -30 since cos-30 will be in the C quadrant, meaning it will be positive whereas cos positive 30 will be in A quadrant meaning all are positive? And similar reasoning applied to sin?

Cos (x) = Cos (-x)

Using your example of 30 degrees: Cos (30) = √3/2. Cos (-30) is the same as the cos (330) which is also √3/2 because cos is positive in the I and IV quadrants, but negative in the II and III quadrants. So with the cos function, any positive angle (30, 50, 180, 250, whatever you pick) will produce the same value as the equivalent negative value.