Remove left sidebar on a POST page

On some of my posts and pages on schoorsteenvegerinfo.com I want to remove the left sidebar.

I know this code from Tyler – WPMU Dev Support:

.singular-post #sidebar-primary {
display: none;
}

.singular-post .content-wrap {
float: left;
width: 100%;
}

.singular-post #content {
width: 75%;
}

.singular-post #sidebar-secondary {
width: 23%;
}

This code however also changes the width of the content part and the right sidebar on MOBILE.

I would like to keep everything as default on mobile. How can I do that?