Reducing Sugars

[Rita]

Hi All,
A prac order asks for starch solution (fairly dilute). Can anyone help me with how 'fairly dilute' is 'fairly dilute in reducing sugars prac'? 0.5%? more? less?
Thanks in advance,
Rita

[bigmack]

My Chem teacher askes for 0.01% ....it will still give a dark blue result with an Iodine test

He was saying the regular 1% starch solution was a giveaway compared to the clear Glucose and Sucrose solutions

[Rita]

Teacher was talking about 5% for sucrose and glucose solutions. Can they be lower also?

[bigmack]

Thanks Rita...just got excited
We normally use 1% Sucrose and glucose solution but the Chem teacher said that the Sucrose should break down to Glucose at close to 100 degC but he could never get it to work .

Just knocked up a few beakers of 5% 1% and 0.2% Sucrose and glucose and stuck them on the hot plate with Benidicts

All the Glucose changed colour at around 70 DegC ...even the 0.2% sample but it took a lot longer .

The 5% Sucrose solution Did noticeably change colour at around 95 deg C...nothing as spectacular but Noticable .
The 1% and 0.2% Sucrose did nothing .

Thanks again Rita ...You solved a puzzle . I might make my Chem teacher happy next time they do this .

Yeah the reason he likes the Starch so diluted is so the three all look the same , otherwise the Kids immediately recognise the starch as the cloudy one .

Now the prep room smells like Toffee

[Rita]

Thanks bigmack you explained what I didn't know.